If the selling price of 10 pens is the same as the cost price of 12 pens then gain per cent is

On selling an article at a certain price a man gains 10%. On selling the same article at double the price, gain per cent is

Bananas are bought at 3 for Rs.2 and sold at 2 for Rs. 3. The gain per cent is

On selling 100 pencils a man gains the selling price of 20 pencils. His gain per cent is

Ravi buys some toffees at 5 for a rupee and sells them at 2 for a rupee. His gain per cent is