Question

A and B can do a task in 15 and 20 days respectively. With the help of C, they finish the work in 8 days. In how much time can C alone do a work twice as large as the first one?

Answer 1

★ Answer

• A and B can do a task in 15 and 20 days respectively.
• With the help of C, they finish the work in 8 days.

Let C takes x days to complete their work.

One day work of A, B and C

→ 1/15 , 1/20 and 1/x

→ 1/15 + 1/20 + 1/x = 1/8

→ 4+3/60 + 1/x = 1/8

→ 7/60 + 1/x = 1/8

→ 7x+60/60x = 1/8

→ 7x+60/15x = 1/2

→ 14x+120 = 15x

→ 15x - 14x = 120

→ x = 120

Afterall, C alone takes 120 days to complete work.

»› Work ratio of A and C are,

→ 15/120

→ 1/8 = 1:8

»› Finally, If C wanna do work twice as large as A then..,

→ 15/120 × 2/2

→ 30/240

Hence,

C alone can take 240 days to complete work which is twice as large as work of A.