Question

how does (-5r^2/15)+(5r^2/2)=25r^2/6?

Answer 1

5/2 - 5/15 = 5/2 - 1/3 = 15/6 - 2/6 = 13/6

so, it does not equal 25/6

However, 5/2 + 5/3 = 25/6

Better check for typos.