A, B and C can do a work in 4 days, 5 days and 10 days respectively. In how many days will they be able to do the work if they work together?

$1\frac{9}{11}$

A can do the work in 4 days.

B can do the work in 5 days.

C can do the work in 10 days.

Now total work = LCM of there time = 20

So, the efficiency of A = 20/4 = 5

B = 20/5 = 4

and C = 20/10 = 2

So, they can finish the work in = 20/(4 + 5 + 10) = $1\frac{9}{11}$