Skill: Solve measurement word problems

Measurement word problems become easier when you:

1. Find the quantities you know and the quantity you need to find.
2. Check the units. Make sure measurements use the same units before combining them.
3. Choose the operation:
   • Add to find a total.
   • Subtract to find what is left or the difference.
   • Multiply for equal groups.
   • Divide to split into equal groups.
4. Write an equation, solve it, and label your answer.

Example

A ribbon is $3$ feet $8$ inches long. Mia uses $1$ foot $11$ inches. How much ribbon is left?

Step 1: Identify the relationship.

We know the total ribbon and the amount used. To find what is left, subtract:

$$\text{ribbon left}=\text{total ribbon}-\text{ribbon used}$$

Step 2: Line up the units.

There are $12$ inches in $1$ foot. We need to subtract the inches and feet separately:

$$3\text{ ft }8\text{ in}-1\text{ ft }11\text{ in}$$

Since $8$ inches is less than $11$ inches, regroup $1$ foot as $12$ inches:

$$3\text{ ft }8\text{ in}=2\text{ ft }20\text{ in}$$

Step 3: Subtract.

$$\begin{aligned} 2\text{ ft }20\text{ in}\\ -1\text{ ft }11\text{ in}\\ \hline 1\text{ ft }9\text{ in} \end{aligned}$$

Step 4: State and check the answer.

Mia has $1$ foot $9$ inches of ribbon left.

Check by adding the used ribbon and the ribbon left:

$$1\text{ ft }11\text{ in}+1\text{ ft }9\text{ in} =2\text{ ft }20\text{ in} =3\text{ ft }8\text{ in}$$

The answer matches the original length, so it is reasonable.