What was the percentage of discount offered ?
A. Profit earned by selling the article for Rs. 252 after giving discount was Rs. 52.
B. Had there been no discount the profit earned would have been Rs. 80.
C. Had there been no discount the profit earned would have been 40%.

I : S.P. = 252, Profit = 52

=> C.P. = 252-52 = 200

Since, we cannot find discount and marked price. I alone is not sufficient.

Similarly, II alone & III alone are insufficient.

I & II : After discount, S.P. = 252, Profit = 52

=> C.P. = 252-52 = 200

Without discount (Discount = 0 & M.P. = S.P.), Profit = 80 => M.P. = S.P. = 200+80 = 280

Thus, discount = 280-252 = 28

Discount % = $$\frac{28}{280}*100 = 10\%$$

Thus, I & II together are sufficient.

I & III : After discount, S.P. = 252, Profit = 52

=> C.P. = 252-52 = 200

Without discount (Discount = 0 & M.P. = S.P.), Profit % = 40%

Profit = $$\frac{40}{200}*100 = 80

M.P. = S.P. = 200+80 = 280

Thus, discount = 280-252 = 28

Discount % = $$\frac{28}{280}*100 = 10\%$$

Thus, I & III are sufficient together.