1.  A does 80% of a work in 20 days. He then calls in B and they together finish the remaining work in 3 days. How long B alone would take to do the whole work?
A. 23 days
B. 37 days
C. 371/2 days
D. 40 days

Answer: Option C

Explanation:

Whole work is done by A in ( 20 x 5 ) = 25 days.
4

Now,

( 1 - 4 ) i.e., 1 work is done by A and B in 3 days.
5 5

Whole work will be done by A and B in (3 x 5) = 15 days.

A's 1 day's work

= 1 , (A + B)'s 1 day's work = 1 .
25 15

Therefore B's 1 day's work = ( 1 - 1 ) = 4 = 2 .
15 25 150 75

So, B alone would do the work in 75 = 37 1 days.
2 2