Fractions of amounts (harder)
Solve problems involving increasingly harder fractions to calculate quantities, including non-unit fractions where the answer is a whole number
What a learner can do afterwards
- Find 3/5 of 20
- Calculate 2/3 of 18 and explain the two-step process (divide then multiply)
- Solve: A bag has 24 sweets, 3/8 are red — how many red sweets?
The lesson
You already know how to find a unit fraction of a number, like 1/4 of something: you just divide. Now you are ready for fractions like 2/3 or 3/5, where the top number is more than 1. There is a simple two-step trick: first divide by the bottom number, then multiply by the top number.
Let's calculate 2/3 of 18. Step 1: divide 18 by 3, the bottom number. 18 divided by 3 is 6. Step 2: multiply that answer by 2, the top number. 6 times 2 is 12. So 2/3 of 18 is 12.
Always divide first, then multiply. If you multiply by the top number first, the numbers get big and harder to work with. Dividing first keeps things small and friendly.
To find a fraction of an amount, divide by the bottom number, then multiply by the top number.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.