Question

4. 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) 20 days (b) 5 days (c) 15 days (d) 10 days​

Answer 1

Answer:

∴ the correct answer is 20 days.

Explanation:

A and B can do a work in 12 days, B and C in 15 days, and C and A in 20 days.

Calculations:

According to the question,

A and B can do the work in 12 days

so, (A + B)’s one day’s work = 1/12

Similarly, (B + C)’s one day’s work = 1/15

and (C + A)’s one day’s work = 1/20

On adding all three,

2(A + B + C)’s one days’ work = (1/12) + (1/15) + (1/20)

⇒ (5 + 4 + 3)/60 = 12/60 = 1/5

⇒ (A + B + C)’s one days’ work = 1/10

A, B and C together can finish the whole work in 10 days.

A, B, and C together can finish twice the whole work in 20 days.

∴ the correct answer is 20 days.