A dishonest trader says to customers that he sells his goods at a cost price, but he uses a false weight and gains 12.5 % as profit. How many grams does he use to weigh 1 kg ?

888.8 g 

Gain % = \(\frac{(Error)}{(True \; value – Error)}\) × 100

Seller uses a weight of 800 gms for 1 kg.

1 kg = 1000 gms.

Error in weight = 1000 – 800 = 200 gms.

According to the formula,

Gain % = [\(\frac{200}{1000-200}\)] × 100

⇒ (\(\frac{200}{800}\)) × 100

⇒ 25%