Mamta allow 4% discount on the marked price of her good and still earns a profit of 20% . What is the cost price of a shirt for her marked at 850?

Sale Price = 0.96 * 850 = $816.

Cost = 0.80 * 816 = $652.80

To find the cost price of the shirt, we need to consider the given discount and profit percentage.

Let's assume the cost price of the shirt is "C".

According to the information given, Mamta allows a discount of 4% on the marked price. To find the selling price, we need to calculate:

Selling Price = Marked Price - (Marked Price * Discount Percentage)

Now, let's calculate the selling price of the shirt:

Selling Price = 850 - (850 * 0.04)
Selling Price = 850 - 34
Selling Price = 816

We know that she earns a profit of 20%. To find the cost price, we need to calculate:

Cost Price = Selling Price / (1 + Profit Percentage)

Now, let's calculate the cost price of the shirt:

Cost Price = 816 / (1 + 0.2)
Cost Price = 816 / 1.2
Cost Price = 680

So, the cost price of the shirt for Mamta is 680.