Question 415832
probability that no head were observed

total no. of events = 3

probability of getting head = 1/2

probability of getting tail = 1/2


= 3C3(1/2)^0 (1/2)^3  

= 1*1*1/8 

= 1/8



you can also use it : 

3C0(1/2)^0 (1/2)^3

= 1/8