# Math Help - Simplifying and volume calculating

1. ## Simplifying and volume calculating

Simplify $\frac{27x}{3xy^2}$ I got 9 somehow....

Simplify $\frac{x-5}{x^2-25}$ I'm just stuck on how to deal with the numbers (-5 and -25)

Simplify $(\sqrt{5}-\sqrt{3})(\sqrt{5}+\sqrt{3})$ I got 2

Total surface area of cylinder X is 25cm^2
Total surface area of cylinder Y is 225cm^2
Height of cylinder X is 5cm
Calculate height of cylinder Y

Volume of Cylinder X is 27cm^3
Calculate volume of Cylinder Y

Again... I have no idea for the method of this volume and height calculating.

2. 1) $\frac{9}{y^2}$

2) $\frac{x-5}{x^2-25} = \frac{x-5}{(x-5)(x+5)}$
$= \frac{1}{x+5}$

3) $(\sqrt{5}-\sqrt{3})(\sqrt{5}+\sqrt{3})$ your answer is correct