Your answer would be 1/8.
The probability for getting a tail one time would be 1/2 because there are only 2 sides of a coin. Since tossing one coin doesn't affect the outcome of tossing the other coins, the probability for getting a tail on all of the coins is 1/2 each. We want this to happen 3 times, so the answer would be 1/2 × 1/2 × 1/2 = 1/8.
I hope this helps!
