Fractions of a quantity

How do we find \(\frac{3}{5}\,of\,20\)

Method 1

Find \(\frac{1}{5}\,of\,20\), then multiply by \(3\).

\[\frac{1}{5}\,of\,20 = 20 \div 5 = 4\]

We need \(\frac{3}{5}\,of\,20\), so we multiply \(4\) by \(3\).

\[\frac{3}{5}\,of\,20 = 4 \times 3 = 12\]

Method 2

Multiply \(\frac{3}{5}\) by \(20\).

\[\frac{3}{5} \times 20 = \frac{3}{5} \times \frac{{20}}{1} = \frac{{60}}{5} = 12\]

Now try this question.

Question

Use either method to find \(\frac{3}{7}\,of\,35\).

The answer is \(15\).

Using Method 1: \(\frac{1}{7}\,of\,35 = 5\), and \(3 \times 5 = 15\).