10 articles are bought for ₹ 40 and are sold at ₹ 5 per article. The profit / loss made is:

1. 25% loss

2. 25% profit

3. 20% loss

4. 20% profit

C.P. of 10 articles = ₹ 40

C.P. of 1 article = ₹ $\dfrac{40}{10}$ = ₹ 4

S.P. of 1 article = ₹ 5

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

Profit = S.P. - C.P.

= ₹ 5 - ₹ 4 = ₹ 1

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

Hence, option 2 is the correct option.