To find the square root of a number, just find out the factors (like make a factor tree--my favorite method!).
When there are two of the same number, you can cross them out and take one out from under the square root sign.
Since you figured out that there is one set of two fives, you may take one five out from under the square root sign and leave the remaining one under it
Giving you the answer that the square root of 125 is
If you determine that in your number you can take two or more sets of numbers out from under the square root sign, you simply multiply those numbers together:
So from the example above, when figuring out the square root of 392, you would come up with 7 times two outside of the root sign, giving you 14, and then the 2 remains under the root sign, leaving you with 14 √2
Similarly, to take the third root, you would just notice what there are 3 instances of, which in this case is 5's. Since there are 3 fives, the third root of 125 would be 5 (with nothing left over, so nothing under the radical sign)
Not bad, huh?