Multiply And Divide Fractions

Multiplying Fractions:

Real life applications where common fractions are multiplied or divided include:

• image reduction
• adapting recipes for larger groups of people.

Steps to multiply fractions are:

• Step 1 - Change mixed numbers to improper fractions
• Step 2 - Multiply the numerators(top numbers) and multiply the denominators (bottom numbers)
• Step 3 - Simplify if needed.

The extra step to divide fractions is to multiply by the reciprocal of the second fraction (that is, turn the second fraction upside and then multiply).

Example One - Image Reduction

An image is reduced to one half of its original size. If the original measurement is 34 cm, what is the new reduced measurement?

12 × 34
= 38 cm

Example Two - Adapting Recipes for Large Groups

A risotto recipe for 5 people uses 2 12 cups of rice. How many cups of rice are required to feed 20 people?

Multiplier
= 20 ÷ 5
= 4

No. of cups of rice
= 2 12 × 4
= 10 cups

Q1. 13 × 25
Q2. 38 × 45
Q3. 2 14 × 3 23

A1. 215
A2. 310
A3. 8 14

Example Three - Gym Training

In a gym the whole 2 12 hour training session is divided into 14 hour parts. How many parts is this?

2 12 ÷ 14
= 52 ÷ 14
= 52 × 41
= 202
= 10 parts

Q1. 67 ÷ 14
Q2. 38 ÷ 12
Q3. 2 45 ÷ 110