120. A, B and C can do a piece of work in 20, 30 and 60 days respectively. In how many days can A do the work if he is assisted by B and C on every third day?

✅ The correct answer is option B.
A’s 2 day’s work =

1
x 2

=
1
.

20
10

(A + B + C)’s 1 day’s work =

1
+
1
+1

=
6
=
1
.

20
30
60
60
10

Work done in 3 days =

1
+
1

=
1
.

10
10
5

Now,
1
work is done in 3 days.

5

Whole work will be done in (3 x 5) = 15 days.