We flip a fair coin 10 times. What is the probability that we get heads in at least 8 of the 10 flips?
10!/[8!*2!*2^10] + 10!/[9!*1!*2^10] + [10!/[10!*0!*2^10] ==[45 + 10 + 1] / 2^10==56 / 2^10==7 / 128
You can also verify it this way:
(10 nCr 8+10 nCr 9+10 nCr 10)/2^10= 7 / 128
