Convert Units Using Ratio Reasoning
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6th Grade Math › Convert Units Using Ratio Reasoning
A car is traveling at $60$ miles per hour. Convert $60\text{ mi/hr}$ to feet per second using $1\text{ mi}=5280\text{ ft}$ and $1\text{ hr}=3600\text{ s}$. Use dimensional analysis so units cancel.
$88\text{ ft/s}$ because $60\dfrac{\text{mi}}{\text{hr}}\times\dfrac{5280\text{ ft}}{1\text{ mi}}\times\dfrac{1\text{ hr}}{3600\text{ s}}=88\dfrac{\text{ft}}{\text{s}}$
$31,680\text{ ft/s}$ because $60\times 5280=31,680\text{ ft/s}$
$105.6\text{ ft/s}$ because $60\times\dfrac{5280}{3600}=105.6\text{ ft/s}$
$1.14\text{ ft/s}$ because $60\times\dfrac{3600}{5280}=1.14\text{ ft/s}$
Explanation
This question tests converting measurement units using ratio reasoning (conversion factors as ratios), unit cancellation (dimensional analysis), and manipulating units in multiplication/division. Converting: use conversion factor as ratio ($1 \text{ mi}=5280 \text{ ft}$ gives $5280 \text{ ft}/1 \text{ mi}$, $1 \text{ hr}=3600 \text{ s}$ gives $1 \text{ hr}/3600 \text{ s}$), multiply: $60 \text{ mi/hr} \times(5280 \text{ ft}/1 \text{ mi}) \times(1 \text{ hr}/3600 \text{ s})=88 \text{ ft/s}$ (mi and hr cancel leaving ft/s). Direction: for compound units like speed, chain conversions to cancel step-by-step. Units multiply/divide: length×length=area (ft×ft=ft²), distance÷time=speed (mi÷hr=mi/hr or mph), units treated algebraically. Example: $60 \text{ mph}$ to ft/sec uses $60 \text{ mi/hr} \times(5280 \text{ ft}/1 \text{ mi}) \times(1 \text{ hr}/3600 \text{ sec})$, mi cancels, hr cancels, result: $(60\times5280/3600) \text{ ft/sec}=88 \text{ ft/sec}$; or $3 \text{ feet}$ to inches: $3 \text{ ft} \times(12 \text{ in}/1 \text{ ft})=36 \text{ inches}$; or area $5 \text{ ft} \times 3 \text{ ft}=15 \text{ ft}^2$ (units multiply: ft×ft=ft² square feet). The correct conversion is $60 \text{ mi/hr} \times(5280 \text{ ft} / 1 \text{ mi}) \times(1 \text{ hr} / 3600 \text{ s}) = 88 \text{ ft/s}$, with miles and hours canceling out. A common error is wrong direction (dividing when should multiply for certain factors), conversion factor wrong (using $5000 \text{ ft/mi}$), units not canceled (leaving mi/ft or similar), arithmetic error ($60\times5280/3600=$ wrong calc), or omitting a factor (forgetting time conversion). Process: (1) identify units (start: mi/hr, target: ft/s), (2) find conversions ($1 \text{ mi}=5280 \text{ ft}$, $1 \text{ hr}=3600 \text{ s}$), (3) set up with cancellation ($60 \text{ mi/hr} \times(5280 \text{ ft}/1 \text{ mi}) \times(1 \text{ hr}/3600 \text{ s}$)), (4) calculate ($60\times5280/3600=88 \text{ ft/s}$), (5) verify units (answer should be in ft/s✓). Dimensional analysis: write conversion factors as fractions with units, multiply so units cancel leaving desired unit.
During practice, Maya runs for $1.5$ hours. Use $1\text{ hr}=60\text{ min}$ to convert $1.5$ hours to minutes, showing unit cancellation.
$90\text{ min}$ because $1.5\text{ hr}\times\dfrac{60\text{ min}}{1\text{ hr}}=90\text{ min}$ (hr cancels)
$150\text{ min}$ because $1.5\times 100=150\text{ min}$
$0.025\text{ min}$ because $1.5\div 60=0.025\text{ min}$
$61.5\text{ min}$ because $1.5+60=61.5\text{ min}$
Explanation
This question tests converting measurement units using ratio reasoning (conversion factors as ratios), unit cancellation (dimensional analysis), and manipulating units in multiplication/division. Converting: use conversion factor as ratio ($1 \text{ hr}=60 \text{ min}$ gives ratio $60 \text{ min}$ per $1 \text{ hr}$), multiply: $1.5 \text{ hr} \times(60 \text{ min}/1 \text{ hr})=90 \text{ min}$ (hr cancels: hr in numerator and denominator divide out leaving min). Direction: larger unit→smaller unit multiply (hr→min: ×60), smaller→larger divide (min→hr: ÷60, or ×(1/60)). Units multiply/divide: length×length=area (ft×ft=ft²), distance÷time=speed (mi÷hr=mi/hr or mph), units treated algebraically. Example: convert $1.5$ hours to minutes using $1 \text{ hr}=60 \text{ min}$, multiply: $1.5 \text{ hr} \times(60 \text{ min} / 1 \text{ hr})=1.5\times60 \text{ min}=90$ minutes (hours cancel); or $3$ feet to inches: $3 \text{ ft} \times(12 \text{ in}/1 \text{ ft})=36$ inches; or area $5 \text{ ft} \times 3 \text{ ft}=15 \text{ ft}^2$ (units multiply: ft×ft=ft² square feet). The correct conversion is $1.5 \text{ hr} \times(60 \text{ min} / 1 \text{ hr}) = 90 \text{ min}$, with hour units canceling out. A common error is wrong direction (dividing when should multiply: $1.5\div60=0.025 \text{ hr}$ instead of min), conversion factor wrong (using $100 \text{ min}/\text{hr}$), units not canceled (answer $90 \text{ hr}\cdot\text{min}$ instead of $90 \text{ min}$), arithmetic error ($1.5\times60=80$), or adds instead of multiplies ($1.5+60=61.5$ nonsense). Process: (1) identify units (start: hr, target: min), (2) find conversion ($1 \text{ hr}=60 \text{ min}$), (3) set up with cancellation ($1.5 \text{ hr}\times(60 \text{ min}/1 \text{ hr}$, hr cancels), (4) calculate ($1.5\times60=90 \text{ min}$), (5) verify units (answer should be in minutes✓). Dimensional analysis: write conversion factors as fractions with units ($60 \text{ min}/1 \text{ hr}$), multiply so units cancel leaving desired unit.
A video is $2.25$ minutes long. Convert $2.25$ minutes to seconds using $1\text{ min}=60\text{ s}$. Show the setup with unit cancellation.
$225\text{ s}$ because $2.25\times 100=225\text{ s}$
$135\text{ s}$ because $2.25\text{ min}\times\dfrac{60\text{ s}}{1\text{ min}}=135\text{ s}$ (min cancels)
$122.25\text{ s}$ because $2.25+120=122.25\text{ s}$
$37.5\text{ s}$ because $2.25\div 60=37.5\text{ s}$
Explanation
This question tests converting measurement units using ratio reasoning (conversion factors as ratios), unit cancellation (dimensional analysis), and manipulating units in multiplication/division. Converting: use conversion factor as ratio (1 min=60 s gives ratio 60 s per 1 min), multiply: 2.25 min×(60 s/1 min)=135 s (min cancels: min in numerator and denominator divide out leaving s). Direction: larger unit→smaller unit multiply (min→s: ×60), smaller→larger divide (s→min: ÷60, or ×(1/60)). Units multiply/divide: length×length=area (ft×ft=ft²), distance÷time=speed (mi÷hr=mi/hr or mph), units treated algebraically. Example: convert 2.25 minutes to seconds using 1 min=60 s, multiply: 2.25 min×(60 s/1 min)=2.25×60 s=135 seconds (minutes cancel); or 3 feet to inches: 3 ft×(12 in/1 ft)=36 inches; or area 5 ft×3 ft=15 ft² (units multiply: ft×ft=ft² square feet). The correct conversion is 2.25 min × (60 s / 1 min) = 135 s, with minute units canceling out. A common error is wrong direction (dividing when should multiply: 2.25÷60=0.0375 min instead of s), conversion factor wrong (using 100 s/min), units not canceled (answer 135 min·s instead of 135 s), arithmetic error (2.25×60=120), or adds instead of multiplies (2.25+120=122.25 nonsense). Process: (1) identify units (start: min, target: s), (2) find conversion (1 min=60 s), (3) set up with cancellation (2.25 min×(60 s/1 min), min cancels), (4) calculate (2.25×60=135 s), (5) verify units (answer should be in seconds✓). Dimensional analysis: write conversion factors as fractions with units (60 s/1 min), multiply so units cancel leaving desired unit.
During practice, Maya runs for 2.5 hours. Convert 2.5 hours to minutes using $1\text{ hr}=60\text{ min}$ and show unit cancellation.
$120\text{ minutes}$ because $2\text{ hr}\times 60=120$
$0.0417\text{ minutes}$ because $2.5\div 60\approx0.0417$
$150\text{ minutes}$ because $2.5\text{ hr}\times\frac{60\text{ min}}{1\text{ hr}}=150\text{ min}$ (hr cancels)
$62.5\text{ minutes}$ because $2.5+60=62.5$
Explanation
This question tests converting measurement units using ratio reasoning (conversion factors as ratios), unit cancellation (dimensional analysis), and manipulating units in multiplication/division. Converting: use conversion factor as ratio (1 hr=60 min gives ratio 60 min per 1 hr), multiply: 2.5 hr×(60 min/1 hr)=150 min (hr cancels: hr in numerator and denominator divide out leaving min). Direction: larger unit→smaller unit multiply (hr→min: ×60), smaller→larger divide (min→hr: ÷60, or ×(1/60)). For example, convert 2.5 hours to minutes using 1 hr=60 min, multiply: 2.5 hr×(60 min/1 hr)=2.5×60 min=150 minutes (hours cancel). The correct conversion is 2.5 hr × (60 min/1 hr) = 150 min, with hour units canceling out. A common error is reversing the direction, like dividing 2.5 by 60 to get about 0.0417 hr instead of multiplying, or ignoring the decimal and using only 2 hr to get 120 min, or adding instead of multiplying like 2.5+60=62.5. The process is: (1) identify units (start: hr, target: min), (2) find conversion (1 hr=60 min), (3) set up with cancellation (2.5 hr×(60 min/1 hr), hr cancels), (4) calculate (2.5×60=150 min), (5) verify units (answer in minutes✓). Dimensional analysis ensures units cancel properly, and common mistakes include arithmetic errors or not handling decimal values correctly.
A bag of trail mix weighs $3$ pounds. Use $1\text{ lb}=16\text{ oz}$ to convert $3$ pounds to ounces, showing unit cancellation.
$64\text{ oz}$ because $3\times 16+16=64\text{ oz}$
$19\text{ oz}$ because $3+16=19\text{ oz}$
$48\text{ oz}$ because $3\text{ lb}\times\dfrac{16\text{ oz}}{1\text{ lb}}=48\text{ oz}$ (lb cancels)
$0.1875\text{ oz}$ because $3\div 16=0.1875\text{ oz}$
Explanation
This question tests converting measurement units using ratio reasoning (conversion factors as ratios), unit cancellation (dimensional analysis), and manipulating units in multiplication/division. Converting: use conversion factor as ratio (1 lb=16 oz gives ratio 16 oz per 1 lb), multiply: 3 lb×(16 oz/1 lb)=48 oz (lb cancels: lb in numerator and denominator divide out leaving oz). Direction: larger unit→smaller unit multiply (lb→oz: ×16), smaller→larger divide (oz→lb: ÷16, or ×(1/16)). Units multiply/divide: length×length=area (ft×ft=ft²), distance÷time=speed (mi÷hr=mi/hr or mph), units treated algebraically. Example: convert 3 pounds to ounces using 1 lb=16 oz, multiply: 3 lb×(16 oz/1 lb)=3×16 oz=48 ounces (pounds cancel); or 2.5 hours to minutes: 2.5 hr×(60 min/1 hr)=150 minutes; or area 5 ft×3 ft=15 ft² (units multiply: ft×ft=ft² square feet). The correct conversion is 3 lb × (16 oz / 1 lb) = 48 oz, with pound units canceling out. A common error is wrong direction (dividing when should multiply: 3÷16=0.1875 lb instead of oz), conversion factor wrong (using 10 oz/lb), units not canceled (answer 48 lb·oz instead of 48 oz), arithmetic error (3×16=42), or adds instead of multiplies (3+16=19 nonsense). Process: (1) identify units (start: lb, target: oz), (2) find conversion (1 lb=16 oz), (3) set up with cancellation (3 lb×(16 oz/1 lb), lb cancels), (4) calculate (3×16=48 oz), (5) verify units (answer should be in ounces✓). Dimensional analysis: write conversion factors as fractions with units (16 oz/1 lb), multiply so units cancel leaving desired unit.
A student walks 1.5 miles to a park. About how many feet is that? Use $1\text{ mi}=5280\text{ ft}$ and show unit cancellation.
$7920\text{ ft}$ because $1.5\text{ mi}\times\frac{5280\text{ ft}}{1\text{ mi}}=7920\text{ ft}$ (mi cancels)
$0.000284\text{ ft}$ because $1.5\div 5280\approx0.000284$
$3520\text{ ft}$ because $5280-1760=3520$
$8800\text{ ft}$ because $1.5\times 6000=9000$ then subtract 200
Explanation
This question tests converting measurement units using ratio reasoning (conversion factors as ratios), unit cancellation (dimensional analysis), and manipulating units in multiplication/division. Converting: use conversion factor as ratio (1 mi=5280 ft gives ratio 5280 ft per 1 mi), multiply: 1.5 mi×(5280 ft/1 mi)=7920 ft (mi cancels: mi in numerator and denominator divide out leaving ft). Direction: larger unit→smaller unit multiply (mi→ft: ×5280). For example, convert 1.5 miles to feet using 1 mi=5280 ft, multiply: 1.5 mi×(5280 ft/1 mi)=1.5×5280 ft=7920 feet (miles cancel). The correct conversion is 1.5 mi × (5280 ft/1 mi) = 7920 ft, with mile units canceling out. A common error is reversing the direction, like dividing 1.5 by 5280 to get about 0.000284 mi, or using approximations like 1.5×6000=9000 then subtracting arbitrarily, or subtracting like 5280-1760=3520. The process is: (1) identify units (start: mi, target: ft), (2) find conversion (1 mi=5280 ft), (3) set up with cancellation (1.5 mi×(5280 ft/1 mi), mi cancels), (4) calculate (1.5×5280=7920 ft), (5) verify units (answer in feet✓). Common conversions to memorize include 1 mi=5280 ft, and mistakes include arithmetic errors with decimals.
A student walks $450$ centimeters in a hallway. Use $1\text{ m}=100\text{ cm}$ to convert $450\text{ cm}$ to meters. Show the setup with units canceling.
$45\text{ m}$ because $450\times\dfrac{1}{10}=45\text{ m}$
$45,000\text{ m}$ because $450\times 100=45,000\text{ m}$
$4.5\text{ m}$ because $450\text{ cm}\times\dfrac{1\text{ m}}{100\text{ cm}}=4.5\text{ m}$ (cm cancels)
$0.45\text{ m}$ because $450\div 1000=0.45\text{ m}$
Explanation
This question tests converting measurement units using ratio reasoning (conversion factors as ratios), unit cancellation (dimensional analysis), and manipulating units in multiplication/division. Converting: use conversion factor as ratio (1 m=100 cm gives ratio 1 m per 100 cm), multiply: 450 cm×(1 m/100 cm)=4.5 m (cm cancels: cm in numerator and denominator divide out leaving m). Direction: smaller unit→larger unit divide (cm→m: ÷100, or ×(1/100)), larger→smaller multiply (m→cm: ×100). Units multiply/divide: length×length=area (ft×ft=ft²), distance÷time=speed (mi÷hr=mi/hr or mph), units treated algebraically. Example: convert 450 centimeters to meters using 1 m=100 cm, multiply: 450 cm×(1 m/100 cm)=450/100 m=4.5 meters (centimeters cancel); or 2.5 hours to minutes: 2.5 hr×(60 min/1 hr)=150 minutes; or area 5 ft×3 ft=15 ft² (units multiply: ft×ft=ft² square feet). The correct conversion is 450 cm × (1 m / 100 cm) = 4.5 m, with centimeter units canceling out. A common error is wrong direction (multiplying when should divide: 450×100=45,000 cm instead of m), conversion factor wrong (using 1 m=10 cm), units not canceled (answer 4.5 cm·m instead of 4.5 m), arithmetic error (450/100=4), or adds instead of multiplies (450+100=550 nonsense). Process: (1) identify units (start: cm, target: m), (2) find conversion (1 m=100 cm), (3) set up with cancellation (450 cm×(1 m/100 cm), cm cancels), (4) calculate (450/100=4.5 m), (5) verify units (answer should be in meters✓). Dimensional analysis: write conversion factors as fractions with units (1 m/100 cm), multiply so units cancel leaving desired unit.
A science lab uses 750 milliliters of solution. Convert 750 mL to liters using $1 \text{ L} = 1000 \text{ mL}$. How many liters is that?
0.075 L
7.5 L
75 L
0.75 L
Explanation
This question tests converting measurement units using ratio reasoning (conversion factors as ratios), unit cancellation (dimensional analysis), and manipulating units in multiplication/division. Converting from milliliters to liters: use the conversion factor as a ratio ($1 \text{ L} = 1000 \text{ mL}$ gives $1 \text{ L}/1000 \text{ mL}$), multiply: $750 \text{ mL} \times(1 \text{ L}/1000 \text{ mL}) = 0.75 \text{ L}$ ($\text{mL}$ cancels leaving $\text{L}$). Direction: smaller unit→larger unit divide ($\text{mL}$→$\text{L}$: ÷1000, or ×(1/1000)). Units multiply/divide: length×length=area ($\text{ft} \times \text{ft} = \text{ft}^2$), distance÷time=speed ($\text{mi} \div \text{hr} = \text{mi/hr}$ or mph), units treated algebraically. Example: convert 3 feet to inches using $1 \text{ ft} = 12 \text{ in}$, multiply: $3 \text{ ft} \times(12 \text{ in}/1 \text{ ft}) = 3 \times 12 \text{ in} = 36 \text{ inches}$ (feet cancel); or 2.5 hours to minutes: $2.5 \text{ hr} \times(60 \text{ min}/1 \text{ hr}) = 150 \text{ minutes}$; or area $5 \text{ ft} \times 3 \text{ ft} = 15 \text{ ft}^2$ (units multiply: $\text{ft} \times \text{ft} = \text{ft}^2$ square feet). The correct conversion is $750 \text{ mL} / 1000 = 0.75 \text{ L}$. A common error is multiplying instead of dividing, like $750 \times 1000 = 750,000$ (way too large), or misplaced decimal (7.5 instead of 0.75). Process: (1) identify units (start: mL, target: L), (2) find conversion ($1 \text{ L} = 1000 \text{ mL}$), (3) set up with cancellation ($750 \text{ mL} \times(1 \text{ L}/1000 \text{ mL}$, mL cancels), (4) calculate ($750/1000 = 0.75 \text{ L}$), (5) verify units (answer should be in liters✓). Dimensional analysis: write conversion factors as fractions with units ($1 \text{ L}/1000 \text{ mL}$), multiply so units cancel leaving desired unit.
A rectangular poster is $8$ inches wide and $2$ feet tall. Convert the height to inches using $1\text{ ft}=12\text{ in}$, then find the area in square inches. (Remember: when you multiply lengths, units multiply.)
$32\text{ in}^2$ because $8\times 2\times 2=32\text{ in}^2$
$96\text{ in}$ because $8\times 12=96\text{ in}$
$192\text{ in}^2$ because $2\text{ ft}\times\dfrac{12\text{ in}}{1\text{ ft}}=24\text{ in}$, then $8\text{ in}\times 24\text{ in}=192\text{ in}^2$
$192\text{ in}$ because $8\text{ in}\times 24\text{ in}=192\text{ in}$
Explanation
This question tests converting measurement units using ratio reasoning (conversion factors as ratios), unit cancellation (dimensional analysis), and manipulating units in multiplication/division. Converting: use conversion factor as ratio (1 ft=12 in gives ratio 12 in per 1 ft), multiply for area: first 2 ft×(12 in/1 ft)=24 in, then 8 in×24 in=192 in² (units multiply: in×in=in²). Direction: larger unit→smaller unit multiply (ft→in: ×12), and remember area units square when multiplying lengths. Units multiply/divide: length×length=area (ft×ft=ft²), distance÷time=speed (mi÷hr=mi/hr or mph), units treated algebraically. Example: convert 2 feet to inches using 1 ft=12 in, multiply: 2 ft×(12 in/1 ft)=24 inches (feet cancel), then area 8 in×24 in=192 in² (units multiply: in×in=in² square inches); or 2.5 hours to minutes: 2.5 hr×(60 min/1 hr)=150 minutes; or area 5 ft×3 ft=15 ft². The correct conversion is 2 ft × (12 in / 1 ft) = 24 in, then 8 in × 24 in = 192 in², with feet canceling and units squaring properly. A common error is wrong direction (dividing height), conversion factor wrong, units not squared (answer 192 in instead of in²), arithmetic error (8×24=180), area units wrong (192 ft² not in²), or adds instead of multiplies. Process: (1) identify units (height: ft to in, then area in in²), (2) find conversion (1 ft=12 in), (3) set up conversion (2 ft×(12 in/1 ft)), (4) calculate area (8×24=192 in²), (5) verify units (answer in square inches✓). Dimensional analysis: write conversion factors as fractions with units, ensure multiplied units result in squared form for area.
A rectangular poster is 8 inches wide and 3 feet tall. First convert the height to inches using $1\text{ ft}=12\text{ in}$, then find the area in square inches. What is the area?
288 in$^2$
24 in$^2$
264 in$^2$
96 in$^2$
Explanation
This question tests converting measurement units using ratio reasoning (conversion factors as ratios), unit cancellation (dimensional analysis), and manipulating units in multiplication/division. Converting height from feet to inches: use the conversion factor as a ratio (1 ft=12 in gives 12 in/1 ft), multiply: 3 ft×(12 in/1 ft)=36 in (ft cancels leaving in), then area: 8 in × 36 in = 288 in² (units multiply to square inches). Direction: larger unit→smaller unit multiply (ft→in: ×12), and for area, ensure both dimensions in same unit. Units multiply/divide: length×length=area (ft×ft=ft²), distance÷time=speed (mi÷hr=mi/hr or mph), units treated algebraically. Example: convert 3 feet to inches using 1 ft=12 in, multiply: 3 ft×(12 in/1 ft)=3×12 in=36 inches (feet cancel); or 2.5 hours to minutes: 2.5 hr×(60 min/1 hr)=150 minutes; or area 5 ft×3 ft=15 ft² (units multiply: ft×ft=ft² square feet). The correct area is 8 in × 36 in = 288 in² after conversion. A common error is not converting units before multiplying, like 8 in × 3 ft = 24 in·ft (mixed units), or wrong arithmetic (8×36=96, too small). Process: (1) identify units (height: ft to in), (2) find conversion (1 ft=12 in), (3) convert (3 ft×12 in/ft=36 in), (4) calculate area (8×36=288 in²), (5) verify units (answer should be in in²✓). Multiplying lengths: ft×ft=ft² (area in square feet), but here convert to in².