At least 3 heads from 4 tosses.

# of 3 heads

# of 4 heads

We can use combination to figure out ways that we can pick 3 out of 4 to have heads

4C3

THen add 4C4 - out of 4, choose all four to have heads.

4C3 + 4C4 = total # combinations

2^4 = total # of variations.

Recall that when it comes to coin flipping, it's just one value. Either heads or tails. It's the same idea as in poker, you get one card value but it has 4 variations (hearts, spade, club, or diamond).

In poker, if you got dealt the same card 4 times, you would be looking at 4^4 variations. But with the coin, we only have 2 states (NOT 4 like in poker). So the variations is 2^4

(4C3 + 4C4) / 2^4

= (4 + 1) / 16

= 5/16

_________________

... and more

What's Inside GMAT Pill?

Zeke Lee, GMAT Pill Study Method (Study Less. Score More.)

GMAT Pill Reviews | GMAT PILL Free Practice Test