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Primary 6 · Ratio · Question type 1.2

P6 Ratio: Equivalent Ratios

Scale both terms by the same factor to write an equivalent ratio or find a missing term.

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Primary 6, on the MOE Primary Mathematics syllabus.

In the Ratio chapter10 question types · see the chapter

The lesson · 2 minutes 55 seconds

How do you find equivalent ratios in P6?

Watch: equivalent ratios, 3 laps against 2 laps

Another worked example

A worked example

Every morning, Daniel runs 3 laps of a track and Rachel runs 2. One day, Rachel has run 8 laps in all. How many laps has Daniel run?

The working · Three lines

The step-by-step working

Written out in full, the way it should appear on paper.

  1. 6 : 4
  2. 3 : 2 (simplest form)
  3. 12 : 8

Daniel has run 12 laps.

Practise · Modelled on top school exam questions

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Find the missing term

Find the missing term, then check that both terms scale together.

The two ratios below are equivalent. 4 : 10 = □ : 45. What number does the box stand for?

Show the step-by-step solution
  1. 4 : 10 = □ : 45
  2. 45 is not a whole number of 10s: 45 ÷ 10 = 4.5
  3. so scale the pair down first, by its highest common factor
  4. highest common factor of 4 and 10 = 2
  5. 4 : 10
  6. ÷ 2 = 2 : 5
  7. the 5 has to reach 45, so the multiplier = 45 ÷ 5 = 9
  8. 2 : 5
  9. × 9 = 18 : 45
  10. missing term = □ = 18

Ans: 18

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