Question

Find the probability that when a fair coin is flipped four times at least 2 heads

Answer 1

Since the problem states "at least" we need to also find probability of 3 H or 4 H or 5 H

Now find the probability of flipping a head 4 times; $\frac{1}{2}$⁴
= (1/16) 

Now probability of flipping a head 3 times: (4C3)(1/2)⁴ = 4/16

Probability of flipping a head 2 times; (4C2)(1/2)⁴=6/16 

(1/16)+(4/16)+(6/16)=11/16

Probability of flipping a fair coin 4 times with at least 2 heads is 11/16.

Hope I helped :)