Mathematics » Introducing Numbers » Multiply Whole Numbers

# Multiplication in Applications

## Multiply Whole Numbers in Applications

We will use the same strategy we used previously to solve applications of multiplication. First, we need to determine what we are looking for. Then we write a phrase that gives the information to find it. We then translate the phrase into math notation and simplify to get the answer. Finally, we write a sentence to answer the question.

### Example

Humberto bought $$4$$ sheets of stamps. Each sheet had $$20$$ stamps. How many stamps did Humberto buy?

#### Solution

We are asked to find the total number of stamps.

 Write a phrase for the total. the product of 4 and 20 Translate to math notation. $$4\cdot 20$$ Multiply. Write a sentence to answer the question. Humberto bought 80 stamps.

### Extra:

Valia donated water for the snack bar at her son’s baseball game. She brought $$6$$ cases of water bottles. Each case had $$24$$ water bottles. How many water bottles did Valia donate?

Valia donated 144 water bottles.

### Extra:

Vanessa brought $$8$$ packs of hot dogs to a family reunion. Each pack has $$10$$ hot dogs. How many hot dogs did Vanessa bring?

Vanessa bought 80 hot dogs.

### Example

When Rena cooks rice, she uses twice as much water as rice. How much water does she need to cook $$4$$ cups of rice?

#### Solution

We are asked to find how much water Rena needs.

 Write as a phrase. twice as much as 4 cups Translate to math notation. $$2\cdot 4$$ Multiply to simplify. 8 Write a sentence to answer the question. Rena needs 8 cups of water for cups of rice.

### Extra:

Erin is planning her flower garden. She wants to plant twice as many dahlias as sunflowers. If she plants 14 sunflowers, how many dahlias does she need?

#### Solution

Erin needs 28 dahlias.

### Extra:

A college choir has twice as many women as men. There are 18 men in the choir. How many women are in the choir?

#### Solution

There are 36 women in the choir.

### Example

Van is planning to build a patio. He will have $$8$$ rows of tiles, with $$14$$ tiles in each row. How many tiles does he need for the patio?

#### Solution

We are asked to find the total number of tiles.

 Write a phrase. the product of 8 and 14 Translate to math notation. $$8\cdot 14$$ Multiply to simplify. $$\begin{array}{r}\stackrel{3}{1}4 \\ ×8 \\ \hline 112 \end{array}$$ Write a sentence to answer the question. Van needs 112 tiles for his patio.

### Extra:

Jane is tiling her living room floor. She will need 16 rows of tile, with 20 tiles in each row. How many tiles does she need for the living room floor?

#### Solution

Jane needs 320 tiles.

### Extra:

Yousef is putting shingles on his garage roof. He will need 24 rows of shingles, with 45 shingles in each row. How many shingles does he need for the garage roof?

#### Solution

Yousef needs 1,080 tiles.

If we want to know the size of a wall that needs to be painted or a floor that needs to be carpeted, we will need to find its area. The area is a measure of the amount of surface that is covered by the shape. Area is measured in square units. We often use square inches, square feet, square centimeters, or square miles to measure area. A square centimeter is a square that is one centimeter (cm.) on a side. A square inch is a square that is one inch on each side, and so on.

For a rectangular figure, the area is the product of the length and the width. The figure below shows a rectangular rug with a length of $$2$$ feet and a width of $$3$$ feet. Each square is $$1$$ foot wide by $$1$$ foot long, or $$1$$ square foot. The rug is made of $$6$$ squares. The area of the rug is $$6$$ square feet.

The area of a rectangle is the product of its length and its width, or $$6$$ square feet.

### Example

Jen’s kitchen ceiling is a rectangle that measures 9 feet long by 12 feet wide. What is the area of Jen’s kitchen ceiling?

#### Solution

We are asked to find the area of the kitchen ceiling.

 Write a phrase for the area. the product of 9 and 12 Translate to math notation. $$9\cdot 12$$ Multiply. $$\begin{array}{r}\stackrel{1}{1}2 \\ ×9 \\ \hline 108\end{array}$$ Answer with a sentence. The area of Jen’s kitchen ceiling is 108 square feet.

### Extra:

Zoila bought a rectangular rug. The rug is 8 feet long by 5 feet wide. What is the area of the rug?

The area of the rug is 40 square feet.

### Extra:

Rene’s driveway is a rectangle 45 feet long by 20 feet wide. What is the area of the driveway?