A can do a work in 15 days. B is 25% more efficient than A. In how many days, working together A and B will complete the same work?

$\frac{20}{3}$

A = 15 days,

B is 25% more efficient than A. therefore,

⇒ A : B = 4 : 5  (Efficiency)

⇒ Total work = 4 x 15 = 60 units,    ..(Efficiency × Days = Total work)

⇒ Time required by A + B to complete the work = \(\frac{60}{4+5}\) = \(\frac{60}{9}\) = \(\frac{20}{3}\) days,     ..(\(\frac{Work}{Efficiency}\) = Time)