Price decreased from 400 to 299.95
We can say,
Old Price = 400
New Price = 299.95
We can use the following formula to find the percentage change (in this case, markdown):

Where
p is the percentage change
New is the New Price
Old is the Old Price
Let's substitute the information we know and find out the answer. Shown below:

Rounding our answer to 2 decimal places, we can say that the customers are offered 25.01% markdown on the price of sports shirt.
Answer