If A : B = 4 : 9, B : C = 3 : 7 and C : D = 5 : 2, find A : B : C : D.

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Accepted Answer

1. Make B common: from $A:B=4:9$ and $B:C=3:7$, scale the second by 3 to get $B:C=9:21$. So $A:B:C=4:9:21$.

2. To match $C$ with $C:D=5:2$, scale $A:B:C$ by $5$ to get $20:45:105$.

3. Scale $C:D$ by $21$ to get $105:42$.

4. Combine to get $A:B:C:D=20:45:105:42$. So the correct choice is (a).

FINAL_ANSWER: a

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