Question

A can do a work in 15 days and B in
20 days. If they work on it together for
4 days, then what is the fraction of the
work that is left?
(A) 1/4
(B)1/10
(C)7/15
(D)8/15
​

Answer 1

D) 8/15

Take LCM of 15 and 20 as the total amount of work which is 60 units in this case.

A can do work in 15 days therefore amount of work done by A in 1 day is 60/15 = 4 units

B can do work in 15 days therefore amount of work done by A in 1 day is 60/20 = 3 units

Total amount of work done in 1 day =A work of 1 day+B's work of 1 day=4 units +3 units=7 units

Amount of work done in 4 days =4*7=28 units

Amount of Work Left = 60–28=32 units

Fraction of work left = Amount of work left/ Total Work = 32/60 = 8/15.

Answer 2

Answer:

D

Step-by-step explanation:

A does 1/15 of work per day

B does 1/20 work per day

each day they do 7/60 work

after four days 28/60 or 7/15 work is done thus 8/15 work is left