Vikas buys an old bike for Rs.30,000 and spends Rs.5,000 on its repairs. If he sells the bike for Rs.42000, his gain percentage is:

Selling price of bike  = Rs 42,000

Cost price of  bike = Rs 30,000 + Rs.5000

Profit = Selling Price - Cost Price

​Solution:​

Cost price = 30,000 + 5,000

= Rs. 35000

Selling price = Rs 42,000

Profit = Rs. (42,000 - 35,000)

= Rs. 7,000

Profit percentage = $$\frac{7000}{35000}$$​ × 100

=  20%

Thus, correct option is (b).