Answer:
1/16
Explanation:
There is a 1/2 chance to flip a heads. 
So, in this case, we would multiply 1/2 four times in reference to the coins being flipped a total of 4 times to find its probability. 
 
1/2 x 1/2 x 1/2 x 1/2 = 1/16 
Thus, there is a 1/16 chance that you'd get heads four times in a row.