A shopkeeper bought some mangoes at a rate of $8$ mangoes for $Rs.5$ and then sold them at a rate of $Rs.9$ per dozen. Find his percentage of profit or loss.

The correct option is A: $20\%$ profit

Cost price of $8$ mangoes (C.P) $=Rs.5$

Selling price of $12$ mangoes $=Rs.9$

So, selling price of $1$ mango $=Rs.\frac{9}{12}=Rs.0.75$

Selling price of $8$ mangoes (S.P)
$=$ Selling price of $1$ mango $\times 8=0.75\times 8=Rs.6$

S.P of $8$ mangoes $>$ C.P of $8$ mangoes, so the shopkeeper has made a profit in this sale.

Profit $=$ Selling Price $-$ Cost Price $=Rs.6-Rs.5=Rs.1$

$\text{Profit}\%=\frac{\text{profit}}{\text{C.P}}\times 100$

$=\frac{1}{5}\times 100=20\%$