Question

Elise tosses a fair coin three times in a row. What is the probability that she gets two heads in a row?

Answer 1

`\textrm{P(2 heads in a row) } =\boxed{(3)/(8)}`

Explanation:

Let H represent the event that the coin turns up heads and T the event that coin turns up tails

So we can get H on the first toss, then 2 T's on the next two tosses, a T on the first toss and 2 H on the next two tosses, two T on the first two tosses and a H on the third toss etc.

The sample space for 3 tosses of a coin consists of 2³ elements since there are two possible outcomes for each of 3 events

The sample space is enumerated below

1 H H H

2 T H H

3 H T H

4 T T H

5 H H T

6 H T T

7 T H T

8 T T T

There are 3 possibilities where 2 H appear in a row

These are the ones in bold in the table above

Since only 3 outcomes out of a total of 8 possible outcomes can result in 2 heads in a row,

`\textrm{P(2 heads in a row) } =(3)/(8)`