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Proportional Reasoning-1

The same comparison in bigger numbers

Squash is a fruit syrup. A small jug uses 3 spoons of squash to 2 of water. A big jug uses 12 to 8. Do they taste the same?

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Ratio 3 : 2, drawn as two bars.
Step 1 of 3
  1. Ratio 3 : 2, drawn as two bars.
  2. Multiply both parts by 4: 12 : 8.
  3. Both divide to 1.5 — same comparison.

The rule

Yes. 12 : 8 is 3 : 2 with both parts multiplied by 4.

Ratios that make the same comparison are equivalent ratios. Multiply both parts by the same number, not zero. The comparison does not change.

  • Take 5 : 4. Multiply both parts by 3: 5 × 3 = 15 and 4 × 3 = 12. That gives 15 : 12.
  • To find ? in 15 : 20 = ? : 80, notice that 20 × 4 = 80. Multiply 15 by 4 too: 15 × 4 = 60.

Watch out!

Adding the same number to both parts usually changes the ratio. Adding 4 to 3 : 2 gives 7 : 6. But 3 ÷ 2 = 1.5, and 7 ÷ 6 is about 1.17.

Jump to lesson

This track

  1. 0 Start here
  2. 1 How much more, and how many times
  3. 2 What 3 : 2 says, and what it does not
  4. 3 The same comparison in bigger numbers
  5. 4 Match the units, then cut it down
  6. 5 Sharing an amount in a ratio
  7. 6 Checkpoint: comparing, writing and sharing
  8. 7 Two ratios that are equal
  9. 8 Find the value of one
  10. 9 When two amounts grow together
  11. 10 A rate is a ratio with units on it
  12. 11 A scale is a ratio you can walk
  13. 12 Checkpoint: proportion, rates and scales
  14. 13 The big picture
  15. 14 Track quiz

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