By selling 45 lemons for Rs 40, a man loses 20%. How many should he sell for Rs 24 to gain 20% in the transaction ?

Let S.P. of 45 lemons be Rs. x.

Then, 80 : 40 = 120 : x or   x =  $\frac{40\times 120}{80}$= 60

For Rs.60, lemons sold = 45

For Rs.24, lemons sold  = $\frac{45}{60}\times 24$= 18.