In this case, we need to make sure each instance is independent of the last. Simply put, the outcome of the second round has no relation to the outcome of the first. They are two different events.

If they are independent, a simple formula can be used. (P)^n, where P is the probability, and n is the number of occurrences.

For 30%, P=0.3
n=36

(0.3^36)* 100 gives you the probability expressed as a percentage.

Since 0.3 can also be represented as 1/3.3bar, you can say

(1/3.333)^36, which simplifies to (1 / 6.6 x 10^18)

Or, the probability is 1 out of every 6.6 x 10^18 times.

You're more likely to win the powerball twice in a row.

What you did is exactly how its done. It's easier to use the exponent button, however.