By selling 45 lemons for ₹ 40 a man loses 20%. How many should he sell for ₹24 to gain 20%?

18

⇒ SP of one lemon = \(\frac{40}{45}\)                 [@20% loss]

⇒ CP of one lemon = \(\frac{40}{45}\) × \(\frac{100}{80}\)

⇒ SP of one lemon = \(\frac{40}{45}\) × \(\frac{100}{80}\) × \(\frac{120}{100}\)                            [@20% profit]

                              = \(\frac{4 × 6}{3 × 6}\)

                              = \(\frac{24}{18}\)

So , SP of 18 lemons = Rs. 24

Therefore, he should sell 18 lemons in Rs.24 to gain 20%