Question

A can do a piece of work in 4 days and B can do the same work in 5 days. Find, how much work can be done by them working together in:
(i) one day
(ii) What part of work will be left, after they have worked together for 2 days?
[4 Marks]

Answer 1

It is given that
A can do a piece of work in 4 days
B can do the same work in 5 days [0.5 Mark]
A’s one day work = $\frac{1}{4}$
B’s one day work = $\frac{1}{5}$ [0.5 Mark]
(i) A and B both one day work = $\frac{1}{4}+\frac{1}{5}$
Taking LCM
= (5 + 4)/ 20
= 9/ 20 [1.5 Marks]

(ii) A and B two days’ work = 9/20 $\times$ 2 = 9/10
So the work left after 2 days = 1 – 9/10
Taking LCM
= (10 – 9)/ 10
= 1/10 [1.5 Marks]