You could make a tree diagram
H T ← 1st toss
H T H T ← 2nd toss
H T H T H T H T ← 3rd toss
etc ,,, then count the combination of favorable outcomes
Using a calculator:
Total number of outcomes is

= 128
Probability of getting exactly 3 heads is found using the follow calculator feature: binompdf(7, 0.5, 3)
ANSWER: Typed into the calculator as follows binompdf(7,0.5,3)×128 =
35