Q) A can finish a work in 45 days and B can do the same work in 40 days. If A and B started working together and after some days A left. B continued working and finished the balance work in 23 days. How many days did A work?

a) 5 days              b) 7 days             c) 9 days                d) 11 days

Ans:

A’s 1 day work = 1/45

B’s 1 day work = 1/40

∴ (A + B)’s 1 day’s work = 1/45 + 1/40 = 17/360

Let’s consider that A left after X days.

∴ work done by (A + B) in X days = 17X /360

∴ Balance work = [1 – 17 X/360] ……… (i)

This work was finished by B in 23 days

∵ Work done by B in 1 day = 1/40

∴ Work done by B in 23 days = 23/40 ….. (ii)

[1 – 17 X/360] =  23/40

∴ 360 – 17 X = 23 x 360/40 = 23 x 9 = 207

∴ 360 – 207 = 17 X

∴ 17 X = 153

∴ X = 153/17 = 9 days

Hence, Answer is [C]

Please do press “Heart” button if you liked the solution.