You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.

Q: Question: A man rows his boat 85 km downstream and 45 km upstream, taking 2 1/2 hours each time. Find the speed of the stream?

 Option A: 6 kmph

 Option B: 9 kmph

 Option C: 3 kmph

 Option D: 8 kmph

 Option E: 1 kmph

A: Option D
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Q: Question: In how many seconds will a train 100 meters long pass an oak tree, if the speed of the train is 36 km/hr?

 Option A: 6

 Option B: 8

 Option C: 10

 Option D: 12

 Option E: 14

A: Option C
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Q: Question: If a train, travelling at a speed of 180 kmph, crosses a pole in 5 sec, then the length of train is?

 Option A: 250 m

 Option B: 112 m

 Option C: 117 m

 Option D: 125 m

 Option E: 123 m

A:
Option A
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