Question

A coin is tossed four times What is the probability of getting four heads? (1 mark) a) b) What is the probability of getting exactly work. (2 marks) two heads? Be sure to show your What is the probability of not getting two heads? Be sure to show your work.

Answer 1

Answer:

1. A coin is tossed four times. What is the probability of getting four heads?

Each toss has a 1/2 chance of getting a head.

So the chance of getting all four heads can be calculated as :

$1/2\times1/2\times1/2\times1/2=1/16$

2. A coin is tossed four times. What is the probability of getting two heads?

Each toss can have 2 results, so 4 flips will have $2^{4}$ or 16 results.

Getting two heads means getting two tails also. So, we can get the number of times two heads come = $\frac{4!}{2!2!}$ = 6

We can write the groups like - {HHTT,HTHT,HTTH,THHT,THTH,TTHH}

So, the required probability is : 6/16 or 3/8.

3. Not getting two heads means getting 3 tails and 1 head or all tails.

Probability of having all tails = $1/2\times1/2\times1/2\times1/2=1/16$

Probability of one head(1st trial) and three tails = 1/16

Probability of one head (2nd trial) and three tails (the 1st, 3rd and 4th trials) = 1/16

Probability of one head (3rd trial) and three tails (the 1st, 2nd and 4th trials) = 1/16

Probability of one head (4th trial) and three tails (the 1st, 2nd and 3rd trials) = 1/16

So, the total probability showing only one or none head and at least three tails = $1/16+1/16+1/16+1/16+1/16=5/16$