The cost price of an article is $\dfrac{4}{5}$ times of its selling price. Find the loss or the gain as percent.

Given:

The C.P. of an article = $\dfrac{4}{5}$ times of its S.P.

Let the S.P. be ₹ $100$.

$\text{C.P.} = ₹ \dfrac{4}{5} \times 100\\[1em] = ₹ \dfrac{400}{5}\\[1em] = ₹ 80$

(∵ S.P. is greater than C.P., means article is sold at gain.)

Gain = S.P. - C.P.

= ₹ 100 - ₹ 80

= ₹ 20

$\text{Gain\%} = \dfrac{\text{Gain}}{\text{C.P.}} \times 100\% \\[1em] = \dfrac{20}{80} \times 100\% \\[1em] = \dfrac{1}{4} \times 100\% \\[1em] = \dfrac{100}{4}\% \\[1em] = 25\%$

Hence, Gain% = 25%