GCSE Mathematics (9-1)

5.2 Ratio, fractions and linear functions — Practise with help

Try each question first. Open a hint if you are stuck, the next step for one concrete move, and the full working only to check.

Warm-up: remember

Answer these from memory. Do not look back at the section.

  1. Write 56\frac{5}{6} with denominator 18.
  2. Share £56 into 7 equal parts. Work out the value of one part.
Check the warm-up
  1. 56=1518\frac{5}{6}=\frac{15}{18}.
  2. 56÷7=856\div7=8, so one part is £8.

If an answer differs, revisit Section 4.1 for equivalent fractions and Section 5.1 for the unitary method.

Practise with help

1. The ratio of red to blue counters is 2:32:3. If the ratio stays the same, how many blue counters go with 8 red counters?

Hint

Set the two ratios equal: 23=8b\frac{2}{3}=\frac{8}{b}.

Next step

The first part grew from 2 to 8, so it was multiplied by 4.

Full working

Multiply the second part by 4: b=3×4=12b=3\times4=12. Check: 8:12=2:38:12=2:3.

2. 4 cakes use 300 g of flour. How much flour do 9 cakes use at the same rate?

Hint

Find the flour for one cake, then multiply.

Next step

One cake uses 300÷4=75300\div4=75 g.

Full working

75×9=67575\times9=675 g. Check the rate: 675÷9=75675\div9=75 g per cake.

3. A straight line passes through (0,0)(0,0) and (4,10)(4,10). Write its equation.

Hint

A line through the origin has equation y=mxy=mx. Find the multiplier mm.

Next step

The multiplier is 10÷4=2.510\div4=2.5.

Full working

The equation is y=2.5xy=2.5x. Check with x=4x=4: 2.5×4=102.5\times4=10.

4. Earlier learning. Write 38\frac{3}{8} as a fraction with denominator 40.

Hint

40÷8=540\div8=5, so multiply the numerator and denominator by 5.

Next step

3×5=153\times5=15.

Full working

38=1540\frac{3}{8}=\frac{15}{40}.

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