alleryIf a : b = 2 : 3 and b : c = 4 : 5, then a : c equals:
A2 : 5
B3 : 4
C8 : 15
D5 : 8
Answer & Solution
Correct answer: C. 8 : 15
1. The two ratios cannot be chained until b means the same amount in both.
2. In the first b is 3 and in the second b is 4, so scale each to their LCM, 12.
3. Multiply the first by 4: a : b = 8 : 12.
4. Multiply the second by 3: b : c = 12 : 15.
5. Now a : b : c = 8 : 12 : 15, so a : c = 8 : 15. Answering 2 : 5 comes from multiplying the outer terms without matching b.
_Source: syllabus Maths, Ch 7 'Comparing Quantities', S7.1 Recalling Ratios and Percentages_
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