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UPCAT Mathematics practice question 33: If a : b = 3 : 4 and b : c = 6 : 7, what is a : c?

Correct answer

A. 9 : 14

Scale the first ratio so b matches: a : b = 9 : 12 and b : c = 12 : 14. Then a : c = 9 : 14.

If a : b = 3 : 4 and b : c = 6 : 7, what is a : c?

  1. 9 : 14Correct
  2. 3 : 7
  3. 18 : 7
  4. 2 : 3

Why A is correct

Scale the first ratio so b matches: a : b = 9 : 12 and b : c = 12 : 14. Then a : c = 9 : 14.

Why the other options are wrong

B 3 : 7
Simply pairs the outer terms of the two given ratios without first scaling b so the two ratios share it.
C 18 : 7
Multiplies a by b's second value instead of scaling both ratios to a common b.
D 2 : 3
An unrelated simplification; no scaling of the shared term was done.
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