Question 256858
"  OK I have a problem: I have the right answer and I've even had it double checked by my teacher I'm just not sure how I got there.
The problem is: 2√5+3√20 And I know the right answer is:8√5.
I just can't remember I got from one to the other. "

Let me see if I can help.

2*sqrt(5) + 3sqrt(20)
2*sqrt(5) + 3sqrt(4*5) --> you can take the 4 out from under the radical since it is the square of 2
2*sqrt(5) + 3*2*sqrt(5)
2*sqrt(5) + 6*sqrt(5)
8*sqrt(5)  --> the answer