Correct Answer: Option D
Part filled in 4 minutes = 4(1/15 + 1/20)
= 7/15.
Remaining part = (1 – 7/15) = 8/15.
Part filled by B in 1 minute = 1/20
So, 1/20 : 8/15 :: 1 : x
x = (8/15 x 1 x 20)
= 10(2/3) min
= 10 min. 40 sec.
Therefore, The tank will be full in (4 min. + 10 min. + 40 sec.)
= 14 min. 40 sec.
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