A shopkeeper bought toffees at a rate of 10 for ₹ 15 and sold them at a rate of 16 for ₹ 40. Find his profit percentage. (correct to two decimal places)

66.67%

According to the question, 

                        quantity          rate 

CP                       10                15      ----(1)

SP                        16                40      ----(2)

Quantity same 

Multiply by 8 in equation 1, and multiply by 5 in equation 2

⇒ CP                    80                  120

⇒ SP                    80                  200

80 toffees CP is 120, and SP is 200

⇒ Profit% = \(\frac{200 - 120}{120}\) × 100

⇒ Profit% = 66.67%