How to multiply decimals

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ACT Math › How to multiply decimals

Questions 1 - 7

A chemistry students needs to dilute some acid. How much water should be added to 2 L of 80% acid solution to yield 50% acid solution?

0.8 L

1.0 L

1.2 L

1.5 L

2.0 L

Explanation

Pure water would be 0% solution and pure solution would be 100%

V1P1 + V2P2 = VfPf

Let x = amount of water to add

x(0) + 2(0.80) = (x + 2)(0.50) which when solved gives x = 1.2 L

Evaluate

$0.5\ast0.05\ast1.5$

Explanation

First, $0.5\ast0.05=0.025$

Then, $0.025\ast1.5=0.0375$

A car has gas mileage of 46 miles per gallon. Assume that gas costs $3.90 per gallon. What would be the total cost of gas if the car traveled 1,150 miles?

$97.50

$100.00

$115.60

$125.70

$179.40

Explanation

First find out how many gallons of gas the car consumed while traveling 1150 miles. This can be found out like so:

1150 miles x gallons/46 miles = 25 gallons

Multiplying 25 by $3.90 yields $97.50.

If , approximately how many inches are in one meter?

Explanation

and $100\ cm=1\ m$

Using the factor-label method we get the following equation.

$\frac{1; meter}{1}*\frac{100 ; cm}{1 ; m}*\frac{1 ; in}{2.5; cm} = 40 ; in$

We treat the units as if they are numbers, and can cancel the units from the fractions.

Kevin is looking at the blueprint of the house he is building. The scale is 1 inch = 5 feet. On paper, the master bedroom is 2.5 inches by 3 inches. What is the actual size of the bedroom?

7.5 ft x 9 ft

15 ft x 25 ft

20 ft x 30 ft

12.5 ft x 15 ft

10 ft x 10 ft