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

Given:

The S.P. of a sofa set = $\dfrac{4}{5}$ times of its C.P.

Let the cost price of sofa set is ₹$100$.

S.P. = ₹$\dfrac{4}{5} \times 100$

= ₹$\dfrac{400}{5}$

= ₹80

(∵ C.P. is greater than S.P., means sofa is sold at a loss.)

Loss = C.P. - S.P.

= ₹100 - ₹80

= ₹20

$\text{Loss\%} = \dfrac{\text{Loss}}{\text{C.P.}} \times 100\%\\[1em] = \dfrac{20}{100} \times 100\%\\[1em] = \dfrac{20}{\cancel{100}} \times \cancel{100}\%\\[1em] = 20\%$

Hence, Sofa is sold at a loss of 20%.