multiply r^2+7r+10/3 by 3r-30/r^2-5r-50

Answer 1

Whenever you have a fraction, you need to enclose the numerator within parentheses.
The same is true of the denominator.
If you omit the parentheses in an exam, you will be marked wrong.

The first expression will be mathematically interpreted as:
r^2+7r+(10/3) because of the priority of multiplication and division over addition and subtraction.

I assume that the expressions have the parentheses inserted:
(r^2+7r+10)/3 * (3r-30)/(r^2-5r-50)

Factorize each expression:

=(r+5)(r+2)/3 * 3(r-10)/((r-10)(r+5))
Cancel out common factors in italics to leave the answer as:
=(r+2)