A fruit-seller buys oranges at 4 for ₹ 8 and sells them at 3 for ₹ 9. Find his profit percent.

C.P. of 4 oranges = ₹ 8

C.P. of 1 orange = ₹ $\dfrac{8}{4}$ = ₹ 2

S.P. of 3 oranges = ₹ 9

S.P. of 1 orange = ₹ $\dfrac{9}{3}$ = ₹ 3

(∵ S.P. is greater than C.P., means oranges are sold at a profit.)

Profit = S.P. - C.P.

= ₹ 3 - ₹ 2 = ₹ 1

$\text{Profit \%} = \dfrac{\text{Profit}}{\text{C.P.}} \times 100\%\\[1em] = \dfrac{1}{2} \times 100\%\\[1em] = \dfrac{100}{2}\%\\[1em] = 50\%$

Hence, the profit percent = $50\%$.