A coin is biased such that the probability of obtaining heads with eac...
Probability of Obtaining Heads with Biased Coin
A biased coin has a probability of obtaining heads with each toss equal to 5. We need to find the probability that the coin is tossed until the first head is obtained.
Part (a): At Least Three Times
To find the probability that the coin is tossed at least three times before obtaining the first head, we can use the geometric distribution. The probability of obtaining the first head on the k-th toss is given by:
P(X=k) = (1-p)^(k-1) * p
where p is the probability of obtaining heads on a single toss, which is equal to 5.
Therefore, the probability of obtaining the first head on or after the third toss is:
P(X>=3) = P(X=3) + P(X=4) + ...
Using the formula above, we can calculate:
P(X>=3) = (1-0.05)^2 * 0.05 + (1-0.05)^3 * 0.05 + ...
We can simplify this using the formula for an infinite geometric series:
P(X>=3) = (1-0.05)^2 * 0.05 / (1 - (1-0.05)) = 0.0476
Therefore, the probability that the coin is tossed at least three times before obtaining the first head is 0.0476.
Part (b): Fewer Than Eight Times
To find the probability that the coin is tossed fewer than eight times before obtaining the first head, we can use the same formula as above and sum up the probabilities for k=1 to k=7:
P(X<8) =="" p(x="1)" +="" p(x="2)" +="" ...="" +="" p(x="">8)>
Using the formula for the probability of obtaining the first head on the k-th toss, we can calculate:
P(X<8) =="" 0.05="" +="" (1-0.05)="" *="" 0.05="" +="" (1-0.05)^2="" *="" 0.05="" +="" ...="" +="" (1-0.05)^6="" *="">8)>
Again, we can simplify this using the formula for an infinite geometric series:
P(X<8) =="" 0.05="" (1-0.95^7)="">8)>
Therefore, the probability that the coin is tossed fewer than eight times before obtaining the first head is 0.2852.