By selling 130 cassettes, a man gains an amount equal to the selling price of 5 cassettes. Find the gain per cent.

Let × be the price of a cassette.

Selling Price of 5 cassettes = 5x.

Selling Price of 130 cassettes = 130x.

Cost Price of 130 cassettes = 130 × – 5x

= 125x

Gain = SP - CP

= 130 × – 125x

= 5x

= 4%