Shanti has enough money to buy 90 pumps worth Rs 500 each. How many pumps can he buy, if he gets a discount of Rs 50 on each pump.

Cost of each pump = Rs.500
So cost of 90 pump = $90\times 500$ = Rs.45000
So total money that Shanti had = Rs.45000
Discount on each pump = Rs.50
So cost of each pump after discount = Rs.500 - Rs.50 = Rs.450
So, number of pumps in Rs.45000 = $\frac{45000}{450}$ = 10
Therefore Shanti can buy 10 pumps.