If you flip a fair coin 7 times, what is the probability that you will get exactly ​2 tails?

There are 2^7 ways of flipping 7 choices. 

There are 7*6/2 = 21 ways of having two heads. 

So I think the answer is 21/2^7 = 21/128

 

I hope this helped. :))

=^._.^=

The probability of exactly two tails is

7C2 (1/2)^7 = 21/128 

since there are 7C2 = 21 ways to choose 2 from 7, and every specific sequence of 7 throws has probability (1/2)^7.