Proportions Math Example 2

Follow the full solution, then compare it with the other examples linked below.

Example 2

medium
If 5 notebooks cost \8.75$, how much do 12 notebooks cost?

Solution

  1. 1
    Set up the proportion: 58.75=12x\frac{5}{8.75} = \frac{12}{x}.
  2. 2
    Cross-multiply: 5x=8.75ร—12=1055x = 8.75 \times 12 = 105.
  3. 3
    Solve: x=1055=21x = \frac{105}{5} = 21.

Answer

$21.00\$21.00
Proportions are useful for unit pricing problems. By setting equivalent ratios of items to cost, you can find the cost for any quantity assuming a constant rate.

About Proportions

An equation stating that two ratios are equal, used to find an unknown when three of the four values are known.

Learn more about Proportions โ†’

More Proportions Examples

Example 1 easy

Solve the proportion [formula].

Example 3 easy

Solve: [formula].

Example 4 hard

A car travels 180 km on 15 litres of fuel. How many litres are needed for a 540 km trip?

Example 5 medium

Solve the proportion: [formula].

โ† All Proportions Examples Proportions Concept