A man bought 30 defective machines for Rs. 1000. He repaired and sold them @ Rs. 300 per machine. He got profit of Rs. 150 per machine. How much did he spend on repairs ?(in Rupees)

Amount spent on buying 30 defective machines = Rs. 1000

Let amount spent on repairs = $$Rs.$$ $$100x$$

=> Total CP = $$Rs.$$ $$(100x+1000)$$

Selling price per machine = Rs. 300

=> Total SP = $$30 \times 300 = Rs.$$ $$9000$$

Profit per machine = Rs. 150

=> Total profit = $$30 \times 150=Rs.$$ $$4500$$

Also, Profit = SP - CP

=> $$4500-(100x+1000)=9000$$

=> $$100x+1000=9000-4500$$

=> $$100x+1000=4500$$

=> $$100x=4500-1000=3500$$

=> $$x=\frac{3500}{100}=35$$

$$\therefore$$ Amount spent on repairs = $$100 \times 35=Rs.$$ $$3500$$

=> Ans - (C)