Ramesh claims that he is selling onions at Rs. 36 per kg, which costs him Rs. 40 per kg, but he gives 800 grams instead of 1 kg. Find Ramesh's percentage gain or loss.

Gain 12.5%

Selling price of 1000 gm = Selling price of 800 gm = Rs. 36

Cost price of 1000 gm = Rs. 40

⇒ Cost price of 800 gm = Rs. \(\frac{40 × 800}{100}\)  = Rs. 32

So, For 800 gm profit = Rs. (36 - 32) = Rs. 4

Profit% = (\(\frac{4}{32}\)) × 100 = 12.5%