In basketball, players often have to take free throws - Leaving Cert Mathematics - Question 8 - 2015
Question 8
In basketball, players often have to take free throws. When Michael takes his first free throw in any game, the probability that he is successful is 0.7.
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Worked Solution & Example Answer:In basketball, players often have to take free throws - Leaving Cert Mathematics - Question 8 - 2015
Step 1
Find the probability that Michael is successful (S) with all three of his first three free throws in a game.
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Answer
To find the probability that Michael is successful in all three free throws, we calculate:
P(S,S,S)=0.7imes0.8imes0.8=0.448
Step 2
Find the probability that Michael is unsuccessful (U) with his first two free throws and successful with the third.
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The probability that Michael is unsuccessful in his first two free throws and successful in the third can be calculated as:
P(U,U,S)=0.3imes0.4imes0.6=0.072
Step 3
List all the ways that Michael could be successful with his third free throw in a game and hence find the probability that Michael is successful with his third free throw.
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The ways for Michael to be successful on his third throw:
Successful on first two throws: S, S, S
Successful on first, unsuccessful on second: S, U, S
Unsuccessful on first two, but successful on third: U, U, S
Calculating the probabilities for each path:
P(S, S, S) = 0.448
P(S, U, S) = 0.7 * 0.2 * 0.6 = 0.084
P(U, U, S) = 0.3 * 0.4 * 0.6 = 0.072
So, the total probability that he is successful on his third free throw:
P=0.448+0.072+0.084=0.604
Step 4
Show that p_{n+1} = 0.6 + 0.2p_n.
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From the provided definitions, we can align as follows:
pn+1=P(S,S)+P(U,S)=pnimes0.8+(1−pn)imes0.6
When simplified:
=pnimes0.8+0.6−0.6imespn=0.6+0.2pn
Step 5
Using the result from part (d) (i) above, or otherwise, show that p = 0.75.
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Assuming for large n, that pn+1ightarrowp and pnightarrowp, we can equate:
p=0.6+0.2p
Solving yields:
ightarrow 0.8p = 0.6
ightarrow p = 0.75 $$
Step 6
Use the ratio a_{n+1} / a_n to show that a_n is a geometric sequence with common ratio 1/5.
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Given that an=p−pn and pn = p thus:
rac{a_{n+1}}{a_n} = rac{p - p_{n+1}}{p - p_n} = rac{0.75 - (0.6 + 0.2p_n)}{0.75 - p_n} = rac{0.15 - 0.2p_n}{0.75 - p_n}
By substitution, as n grows, this ratio approaches 1/5. Thus confirmed the geometric sequence.
Step 7
Find the smallest value of n for which p - p_n < 0.00001.
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Converting the sequence:
a1=p−p1=0.75−0.75=0.05
Then apply for limit convergence:
0.05(1/5)n−1<0.00001
Taking logarithms:
(n−1)ln(1/5)<ln(0.00001)−ln(0.05)
Results:
ightarrow n = 7 $$
Step 8
Based on this knowledge, what is your estimate of the probability that Michael will be successful with his next free throw in the game?
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Given his previous success rate, the best estimate of success would be:
0.75 or p
Step 9
Why would it not be appropriate to consider Michael's subsequent free throws in the game as a sequence of Bernoulli trials?
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This is because events are not independent; the outcome of one throw influences the probability of success in the subsequent throws.
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