问问?没看懂咋算出来的答案?Question #4:A cyclist bikes from town A to tow

问问?没看懂咋算出来的答案?
Question #4:A cyclist bikes from town A to town B and back to town A in 3 hours.He bikes from A to B at a speed of 15 miles/hour,while his return speed is 10 miles/hour.What is the distance between the 2 towns?
(a) 18 miles
(b) 15 miles
(c) 12 miles
(d) 10 miles
(e) 11 miles
Answer:The total time t = tAB + tBA = dAB/(15 miles/hour) + dAB/(10 miles/hour) = dAB/(6 miles/hour).
dAB = dAB/(6 miles/hour) · 3 hours = 18 miles.
(a) is the correct answer.
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