A fair coin is tossed ten times in a row.
What is the probability that "heads" comes up at least eight times?
I got an answer of 7/128, but I lost the paper with the work I showed. Can someone refresh my memory please?
at least 8 times ----> exactly 8 times + exactly 9 times + exactly 10 times
8 times : C(10,8) (1/2)^8(1/2)^2 = 45/1024
9 times : C(10,9)(1/2)^9(1/2) = 10/1024
10 times : C(10,10)(1/2)^10 = 1/1024
so prob(heads at least 8 times) = 56/1024 = 7/128