Q.):-  Raghav has enough money to buy 75 machines worth Rs. 200 each.  How many machines can he buy if he gets a discount of Rs. 50 on each machine?

lesser the price per machine more the machines he can buy
Thus direct proportion
Price / machine * No of machines is a constant
Rs 75* 200 ( 75 machines at 200 per machine)
Discount of Rs 50 per machine price per machine is Rs 200 - 50 = Rs 150
Let us say he buys x machines
He thus pays
Rs 150 * x  which should be equal to Rs 75 * 200
150x = 75* 200
x = 75*200/150 = 100

Thus he can buy 100 machines