a. Copy and complete the table, and use it to construct a tree diagram.

[tex]\[
\begin{tabular}{|c|c|c|}
\hline & Good shot & Bad shot \\
\hline Right club & $\frac{2}{3}$ & $\frac{1}{3}$ \\
\hline Wrong club & $\frac{1}{4}$ & $\frac{3}{4}$ \\
\hline
\end{tabular}
\][/tex]

b. At one short hole, she can reach the green in one shot if it is 'good'. If her first shot is 'bad', it takes one more 'good' shot to reach the green. Find the probability that she reaches the green in at most two shots.



Answer :

Sure, let's work through this problem step by step.

a) Completing the Table

First, we complete the given table with the provided probabilities. The table initially looks like this:

| | Good shot | Bad shot |
|---------------|-----------|----------|
| Right club | 2/3 | ? |
| Wrong club | ? | 3/4 |

We need to fill in the missing probabilities.

- For the right club:
- The probability of a good shot with the right club is [tex]\( \frac{2}{3} \)[/tex].
- Therefore, the probability of a bad shot with the right club is [tex]\( 1 - \frac{2}{3} = \frac{1}{3} \)[/tex].

- For the wrong club:
- The probability of a bad shot with the wrong club is [tex]\( \frac{3}{4} \)[/tex].
- Therefore, the probability of a good shot with the wrong club is [tex]\( 1 - \frac{3}{4} = \frac{1}{4} \)[/tex].

Now the complete table looks like this:

| | Good shot | Bad shot |
|---------------|--------------|-------------|
| Right club | [tex]\( \frac{2}{3} \)[/tex] | [tex]\( \frac{1}{3} \)[/tex] |
| Wrong club | [tex]\( \frac{1}{4} \)[/tex] | [tex]\( \frac{3}{4} \)[/tex] |

Also, since she chooses the clubs randomly, the probability of choosing the right club among 5 clubs is [tex]\( \frac{1}{5} \)[/tex], and the probability of choosing the wrong club is [tex]\( 1 - \frac{1}{5} = \frac{4}{5} \)[/tex].

b) Probability of Reaching the Green in At Most Two Shots

We will now use a tree diagram approach to solve this.

1. First Shot:

- She could choose the right or wrong club.
- For the right club:
- Probability of a good shot [tex]\( = \frac{1}{5} \times \frac{2}{3} = \frac{2}{15} \)[/tex]
- Probability of a bad shot [tex]\( = \frac{1}{5} \times \frac{1}{3} = \frac{1}{15} \)[/tex]

- For the wrong club:
- Probability of a good shot [tex]\( = \frac{4}{5} \times \frac{1}{4} = \frac{1}{5} \)[/tex]
- Probability of a bad shot [tex]\( = \frac{4}{5} \times \frac{3}{4} = \frac{3}{5} \)[/tex]

The probability that she reaches the green in one good shot (first shot):
[tex]\[ P(\text{green in one shot}) = \frac{2}{15} + \frac{1}{5} = \frac{2}{15} + \frac{3}{15} = \frac{5}{15} = \frac{1}{3} \][/tex]

2. Second Shot (if the first shot is bad):

- For the right club chosen initially:
- Probability of a bad shot followed by a good shot:
[tex]\[ \frac{1}{5} \times \frac{1}{3} \times \frac{2}{3} = \frac{1}{5} \times \frac{2}{9} = \frac{2}{45} \][/tex]

- For the wrong club chosen initially:
- Probability of a bad shot followed by a good shot:
[tex]\[ \frac{4}{5} \times \frac{3}{4} \times \frac{1}{4} = \frac{4}{5} \times \frac{3}{16} = \frac{3}{20} \][/tex]

The probability that she reaches the green in two shots:
[tex]\[ P(\text{green in two shots}) = \frac{2}{45} + \frac{3}{20} \][/tex]

Convert [tex]\(\frac{3}{20}\)[/tex] to a common denominator with [tex]\( \frac{2}{45} \)[/tex]:
[tex]\[ \frac{3}{20} = \frac{27}{180}, \quad \frac{2}{45} = \frac{8}{180} \][/tex]
[tex]\[ \frac{8}{180} + \frac{27}{180} = \frac{35}{180} = \frac{7}{36} \][/tex]

Now, combining the probabilities from one and two shots:
[tex]\[ P(\text{green in at most two shots}) = \frac{1}{3} + \frac{7}{36} = \frac{12}{36} + \frac{7}{36} = \frac{19}{36} \][/tex]

So, summarizing:

- [tex]\(P(\text{good shot with right club}) = \frac{2}{3}\)[/tex]
- [tex]\(P(\text{bad shot with right club}) = \frac{1}{3}\)[/tex]
- [tex]\(P(\text{good shot with wrong club}) = \frac{1}{4}\)[/tex]
- [tex]\(P(\text{bad shot with wrong club}) = \frac{3}{4}\)[/tex]
- [tex]\(P(\text{choosing right club}) = \frac{1}{5}\)[/tex]
- [tex]\(P(\text{choosing wrong club}) = \frac{4}{5}\)[/tex]
- [tex]\(P(\text{green in one shot}) = \frac{1}{3}\)[/tex]
- [tex]\(P(\text{green in two shots}) = \frac{7}{36}\)[/tex]
- Total probability of reaching the green in at most two shots:
[tex]\[ P(\text{at most two shots}) = \frac{19}{36} = 0.52778... \][/tex]

So the probability that she reaches the green in at most two shots is [tex]\( \approx 0.528 \)[/tex].