Fractions of Amounts (Cambridge International IGCSE Maths)

Fractions of amounts

How do I find a fraction of an amount?

• Method 1 Divide by the denominator and multiply by the numerator

  • To find $\frac{1}{3}$ of $90$, divide it by 3

    • $90\div3=30$

  • To find $\frac{2}{5}$ of $60$, divide it by 5 then multiply it by 2

    • $60\div5=12$, then $12\times2=24$

• Method 2 Change the fraction into a decimal, then multiply

  • To find $\frac{1}{4}$ of $16$, turn $\frac{1}{4}$ into $0.25$ then multiply

    • $0.25\times16=4$

  • To find $\frac{9}{10}$ of $15$, turn $\frac{9}{10}$ into $0.9$ then multiply

    • $0.9\times15=13.5$

• Method 3 Write both numbers as fractions and multiply two fractions together

  • To find $\frac{2}{3}$ of $60$, write $60$ as $\frac{60}{1}$

    • work out $\frac{2}{3}\times\frac{60}{1}=\frac{120}{3}=40$

  • To find $\frac{5}{6}$ of $\frac{8}{3}$

    • work out $\frac{5}{6}\times\frac{8}{3}=\frac{40}{18}=\frac{20}{9}$