Hi Ashutosh, 
The formula you are referring to is for profit percentage, here we are talking about discount. 
$$\left(1-\frac{x}{100}\right)\left(1-\frac{y}{100}\right)\ =\ 1-\frac{x}{100}-\frac{y}{100}+\frac{xy}{10000}$$
Which would be the same as giving a discount of $$\left(\frac{x}{100}+\frac{y}{100}-\frac{xy}{10000}\right)\times\ 100$$ percent
or simply$$x+y-\frac{xy}{100}$$ percent
The formula in the dashboard refers to profit where both x and y will be positive, hence both xy will have the same sign as x and y. 
The same would not be true in case of discount. 
Hope this help your doubt!
Please feel free to ask any further questions you might have
Regards