(d) Let the person have Rs.100. For Rs.100, he can purchase either 50 oranges or 40 mangoes, i.e., cost of one orange =Rs.2
and cost of one mango =Rs.2.50. Now he keeps Rs.10 for taxi fare and buys 20 mangoes for which he pays Rs.50.
He is left with Rs.40 with which he can buy 20 oranges.