Does this problem have a shortcut ?
I don’t know if this will be quick but to get the product of x and y = 2475(5 in the unit digit) one of the numbers either x or y should have 5 in its unit digit too.
Now, x+y = 100 and we want one of those (can be both to have unit digit as 5).
Now we can easily calculate that 50 * 50 is 2500 —> Thus, we will make a smart guess and choose 45 as x and because x+y = 100, y= 55
So, x * y = 2475 and x+y = 100
sqrt(((x+y)^2)-4xy)
sqrt(10000-9900)
10