find selling price when

1.market price=Rs 990 and discount=10%.

After a 10% discount you still have to pay 90% of the original 990
so
990(.9) = ?

please answer this

Are you telling me you don't know how to take 90% of 990?
(I even showed you the calculation to do!)

To find the selling price after a 10% discount on a market price of Rs 990, you need to multiply the market price by the discount percentage.

So, the calculation would be:
Selling price = Market price - (Market price * Discount percentage)
= Rs 990 - (Rs 990 * 10%)
= Rs 990 - (Rs 990 * 0.10)
= Rs 990 - Rs 99
= Rs 891

Therefore, the selling price after a 10% discount on a market price of Rs 990 would be Rs 891.