Put the following four numbers in order from least to greatest: $A.\ 4 \cdot \sqrt{5}\\ B.\ 6 \cdot \sqrt{2}\\ C.\ 5 \cdot \sqrt{3}\\ D.\ 9$

Method 1: Turn them all into approximate decimals using your calculator, then order them.

Method 2: Change them so each one is total inside a square root. Then order them

e.g. 6sqrt2 = sqrt (36*2) = sqrt (72)