# 9. A completes 80% of a work in 20 days. Then B also joins and A and B together finish the remaining work in 3 days. How long does it need for B if he alone completes the work? A. 37 ½ days B. 22 days C. 31 days D. 22 days

2
by ekalavyaachanta

2015-04-21T16:57:55+05:30

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Let the work be X amount.
So  A does  80% of X  in 20 days.  =>  0.80 * X in 20 days.
in one day  A does  0.80A / 20 = 0.04 X  amount of work

A  and  B  together complete 20% of X amount of work in 3 days.
So their productivity is :  0.20 X / 3  per day.

Productivity of B =  0.20 X/3 - 0.04 X =   0.08 X / 3    per day

B does the complete  work X in :  3 / 0.08 = 37.5 days

2015-04-21T17:52:23+05:30
B alone completes the work in 37.5 days