Question

A and b each working alone can do a work in 15 days and 25 days respectively. they started the work together but b left after some time and a finished the remaining work in 7 days. after how many days from the started did b leave?

Answer 1

$\frac{x - 7 }{25} + \frac{x}{15} = 1 \\ x = 12days$
so 12-7=5days after which b left work