a) $$1\frac{1}{3}$$ hours
b) 2 hours
c) $$2\frac{2}{3}$$ hours
d) $$1\frac{2}{3}$$ hours
Answer: a
Explanation: Ratio of speed = 3 : 4
Ratio of time taken = 4 : 3 (As Speed ∝ $$\frac{1}{{{\text{Time}}}},$$ When distance remains constant.)
Let time taken by A and B be 4x and 3x hour respectively.
4x – 3x = $$\frac{{20}}{{60}}$$
x = $$\frac{{1}}{{3}}$$
Hence, time taken by A = 4x
hours = 4 × $$\frac{1}{3}$$ = $$1\frac{1}{3}$$ hours.
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