A man bought pens at the rate of 12 for Rs. 8 and sold them at the rate of 4 for Rs. 6. His gain % in a transaction is? 

125%

            Price             Qty.

Buy:       8                  12    ..........(i)

Sell        6                    4    ..........(ii)

(i) × 1 and (ii) × 3, (to make qty equal)

            Price             Qty.

Buy:       8                  12

Sell        18                 12

Cost price of 12 = Rs.8

Selling price of 12 = Rs.18

Profit = 18 - 8 = 10

Profit percent =  \(\frac{10}{8}\)× 100 =  \(\frac{5}{4}\)× 100 = 125%