simplify the following radical: the square root of 5 times the square root of 15

Question

I'm familiar with radicals so I do know how to solve them, but when I put this in the calculator I get a different answer than I had originally had, so maybe please explain how you got to the final answer? Thank you.

Answer 1

√5 · √15 = √(5·15) = √75 = √(25·3) = 5√3