A child with a measuring tape near a long friendly snake

The Snake That Needed Measuring

Zoe's pet snake is 4 feet long. The vet's chart only uses inches. How many inches long is the snake?

4th Grade Math

Step 1: Find the Rule

This blue box shows 1 foot. Count the orange inch squares inside it. The count gives us the conversion rule for feet and inches.

There are 12 inch squares inside 1 foot. So 1 foot is 12 times as long as 1 inch.

Step 2: Use the Rule 4 Times

0

12

24

36

48

The snake is 4 feet long. Each foot adds another multiple of 12 on the line. What is the product of 4 × 12?

4 × 12 = 48, so the 4-foot snake is 48 inches long. Adding 4 + 12 = 16 is a trap. We multiply, not add!

Let's Remember

Big Unit to Small Unit: Multiply!

          Step 1: Find the rule (1 ft = 12 in).

          Step 2: Multiply by that number.

          Step 3: Label your answer with the small unit.

Zoe Feet are big and inches are small. It takes many small units to fill one big unit. That is why we multiply!

Finish the Conversion Table

We can generate a table to show the feet and inches pattern.

Feet	Inches
1	12
2	24
3	?

3 × 12 = 36 inches. The inches column counts by 12: 12, 24, 36, 48, and so on.

Watch Out!

A Common Mistake

          Leo wrote: 3 meters = 30 centimeters. That is wrong!

          The rule is 1 m = 100 cm, not 10.

          So 3 m = 3 × 100 = 300 cm.

Always determine the correct rule first. Then multiply. A wrong rule ruins the whole answer!

Solve It!

Rule: 1 kilometer = 1,000 meters.

6 km = ? m

6 × 1,000 = 6,000 meters. Kilometers are big, meters are small, so we multiply by 1,000.

Word Problem

A bag of rice weighs 5 kilograms. The recipe card lists amounts in grams. Rule: 1 kg = 1,000 g. How many grams does the bag weigh?

5 × 1,000 = 5,000 grams. Each kilogram holds 1,000 grams, and there are 5 of them.

Time Conversion

Rule: 1 hour = 60 minutes.

3 hours = ? minutes

3 × 60 = 180 minutes. Think of the pattern: 60, 120, 180.

Word Problem

Mateo fills a fish tank with 2 liters of water. The tank label uses milliliters. Rule: 1 L = 1,000 mL. How many milliliters did he pour?

2 × 1,000 = 2,000 milliliters. Liters are the big unit, so multiply by 1,000.

Weight Conversion

Rule: 1 pound = 16 ounces. Careful, this rule is not 12!

2 lb = ? oz

2 × 16 = 32 ounces. The answer 24 uses the feet rule of 12 by mistake. Pounds use 16!

Challenge!

A movie lasts 2 hours 30 minutes. This takes two steps. First convert the hours, then add the extra minutes. How many minutes in all?

Step 1: 2 × 60 = 120 minutes. Step 2: 120 + 30 = 150 minutes. Writing 230 just sticks the numbers together!

Compare feet and meters: both are big units. When would you need to convert units in your own life?

Great Work!

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correct

rule multiple product pattern generate determine