IBDP Maths SL 4.11 Formal definition and use of the formulae AA HL Paper 1- Exam Style Questions- New Syllabus
Andre will play in the semi-final of a tennis tournament.
If Andre wins the semi-final he will progress to the final. If Andre loses the semi-final, he will not progress to the final.
If Andre wins the final, he will be the champion.
The probability that Andre will win the semi-final is \( p \). If Andre wins the semi-final, then the probability he will be the champion is 0.6.
(a) Complete the values in the tree diagram. [1]
The probability that Andre will not be the champion is 0.58.
(b) Find the value of \( p \). [2]
(c) Given that Andre did not become the champion, find the probability that he lost in the semi-final. [3]
▶️ Answer/Explanation
Complete the tree diagram:
- Probability of winning the semi-final: \( p \)
- Probability of losing the semi-final: \( 1 – p \)
- If wins semi-final, probability of winning the final: 0.6
- If wins semi-final, probability of losing the final: \( 1 – 0.6 = 0.4 \)
- If loses semi-final, no final, so probabilities are not applicable (0 for champion, 1 for not champion, but tree ends).
Probability of not being champion = \( p \cdot 0.4 + (1 – p) \cdot 1 = 0.58 \)
Solve: \( 0.4p + 1 – p = 0.58 \)
\( 1 – 0.6p = 0.58 \)
\( 0.6p = 0.42 \)
\( p = \frac{0.42}{0.6} = 0.7 \)
\(\boxed{0.7}\)
Given not champion, use conditional probability:
Total probability not champion = 0.58
Probability lose semi-final and not champion = \( (1 – p) \cdot 1 = 0.3 \) (since \( p = 0.7 \))
Probability win semi-final and lose final = \( p \cdot 0.4 = 0.7 \cdot 0.4 = 0.28 \)
Probability lose semi-final given not champion = \(\frac{0.3}{0.58} \approx 0.5172\)
\(\boxed{\frac{15}{29}}\)
In a class of 30 students, 19 play tennis, 3 play both tennis and volleyball, and 6 do not play either sport.
The following Venn diagram shows the events “plays tennis” and “plays volleyball”.
The values \( t \) and \( v \) represent numbers of students.
(a) (i) Find the value of \( t \).
(ii) Find the value of \( v \). [4]
(b) Find the probability that a randomly selected student from the class plays tennis or volleyball, but not both. [2]
▶️ Answer/Explanation
Number of students playing only tennis is total tennis players minus those playing both: \( t + 3 = 19 \).
\( t = 19 – 3 = 16 \)
\(\boxed{16}\)
Total students = only tennis + only volleyball + both + neither.
\( t + v + 3 + 6 = 30 \), substitute \( t = 16 \): \( 16 + v + 3 + 6 = 30 \).
\( v + 25 = 30 \)
\( v = 5 \)
\(\boxed{5}\)
Number of students playing tennis or volleyball but not both = only tennis + only volleyball = \( t + v = 16 + 5 = 21 \).
Probability = \(\frac{21}{30} = \frac{7}{10}\)
Alternatively, total students minus (both + neither) = \( 30 – (3 + 6) = 21 \), probability \(\frac{21}{30} = \frac{7}{10}\).
\(\boxed{\frac{7}{10}}\)