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).

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Example One - Image Reduction

An image is reduced to one half of its original size. If the original measurement is ³⁄₄ cm, what is the new reduced measurement?

Answer:
¹⁄₂ × ³⁄₄
= ³⁄₈ cm

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Example Two - Adapting Recipes for Large Groups

A risotto recipe for 5 people uses 2 ¹⁄₂ cups of rice. How many cups of rice are required to feed 20 people?

Answer:
Multiplier
= 20 ÷ 5
= 4

No. of cups of rice
= 2 ¹⁄₂ × 4
= 10 cups

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Dividing Fractions:

Example Three - Gym Training

In a gym the whole 2 ¹⁄₂ hour training session is divided into ¹⁄₄ hour parts. How many parts is this?

Answer:
2 ¹⁄₂ ÷ ¹⁄₄
= ⁵⁄₂ ÷ ¹⁄₄
= ⁵⁄₂ × ⁴⁄₁
= ²⁰⁄₂
= 10 parts