The sqrt function has the distributive property.
So sqrt(a/b) = sqrt(a) / sqrt(b).
In this case, a = 81, and b = 625.
sqrt(81) = 9.
sqrt(625) = 25.
So sqrt(81/625) = 9 / 25.
To get a decimal representation, multiply by a form of 1 that makes the denominator a power of 10. Here, 25 * 4 = 100, so
9/25 * 4/4 = 36/100 = 0.36
