Question

1. A weighted coin is biased so that a head is twice as likely to occur as a tail. If the coin is tossed 4 times, what is the probability of getting at least 1 head? **Hint: Given that the coin is biased, what is the probability of getting heads on a toss? Of getting tails? Use these probabilities in your calculations\.\**

Answer 1

80/81

Explanation:

If a head is twice as likely to occur as a tail, then the probability of getting heads is 2/3 and the probability of getting tails is 1/3.

The probability of getting at least 1 head involves 4 scenarios:

1) 1 Head and 3 Tails

2) 2 Heads and 2 Tails

3) 3 Heads and 1 Tail

4) 4 Heads

Instead of calculate all these scenarios, you could calculate the opposite scenario: 4 Tails. The sum of all possible scenarios is 1, so:

P(at least one head) + P(no heads) = 1

Then, P(at least one head) = 1 - P(no heads)

The probability of 4 tails is:

P(no heads) = P(TTTT) = (1/3)(1/3)(1/3)(1/3)=1/81

Then, P(at least one head) = 1 - 1/81=80/81