Probability of getting a tails on one flip is 1/2
Probability of getting all tails for 10 flips is
(1/2)^10 = 1/1024 = 0.000976
Probability of getting a heads on one flip is 1/2
Probability of getting all heads for 10 flips is
(1/2)^10 = 1/1024 = 0.000976
Probability of getting atleast one tails is
1 - P(no tails) = 1 - P(all heads) = 1 - 0.00098 = 0.999