Question

A and B can do a piece of work in 12 days, C and A in 20 days and B and C in 15 days, then in how many days will they finish it working together?
a)20days
b)5days
c)15days
d)10days​

Answer 1

10 days

Step-by-step explanation:

A and B can do a piece of work in 12 days

It means A and B can do 1/12 of work in one day.

C and A in 20 days

B and C in 15 days

(A+B) + (C+A) + (B+C) = 2 (A+B+C)

$\frac{1}{12} + \frac{1}{20} + \frac{1}{15} = \frac{12}{60} = \frac{1}{5}$

If 2 (A+B+C) = 5 days

A + B + C = 5 * 2 = 10 days

(Time is inversely proportional to manpower. so we multiply 2 with 5 days.)