A man who can swim 48 metres per minute in still water swims 200 metres against the current and 200 metres with the current. If the difference between these two times is 10 minutes, what is the speed of the current?
A30 metres per minute
B31 metres per minute
C29 metres per minute
D32 metres per minute ✓ Correct
Correct answer: (D) 32 metres per minute
Explanation
The current speed is 32 metres per minute.
with current speed c, times are 200/(48-c) and 200/(48+c).
200/(48-c) - 200/(48+c) = 10.
this gives 400c = 10(2304 - c^2).
c^2 + 40c - 2304 = 0.
c = 32 metres per minute.
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