There is a 5/6 chance of failure on each roll. Multiply that number by itself roll each successive roll.
EXACTLY 1 five in six rolls equals the prob of 1 success times the prob of fail/fail/fail/fail/fail.
that's (1/6)(5/6)(5/6)(5/6)(5/6)(5/6) X 6
the final X 6 is because you don't care which of the six rolls is a success.
apologies in advance for typos. I'm on my iPad. I hate typing on it.
Sigh....