A, B and C together can finish a piece of work in 4 days, A alone can do it in 12 days and B alone in 18 days. How many days will be taken by C to do it alone?

9 days

Step-by-step explanation:

A = 1/12 = .083333 completed each day

B = 1/18 = .055555 completed each day

C = 1/x                     completed each day

Finished piece 1/4 = .25 completed each day

A + B + C  = .25

.08333 + .05555  + C = .25

.138888 + C = .25

C = .25 - .138888

C = .11111

C = 1/x

.1111111 = 1/x

.1111111x = 1

x = 9

It will take C 9 days to finish a piece of work alone.

step-by-step explanation: