IB Mathematics SL 4.7 Concept of discrete random variables AI SL Paper 1- Exam Style Questions- New Syllabus
Question
In a game, balls are thrown to hit a target. The random variable \(X\) is the number of times the target is hit in five attempts. The probability distribution for \(X\) is shown in the following table.
\(x\) | 0 | 1 | 2 | 3 | 4 | 5 |
---|---|---|---|---|---|---|
\(P(X=x)\) | 0.15 | 0.20 | \(k\) | 0.16 | \(2k\) | 0.25 |
(a) Find the value of \(k\). [2]
The player has a chance to win money based on how many times they hit the target.
The gain for the player, in \($\), is shown in the following table, where a negative gain means that the player loses money.
\(x\) | 0 | 1 | 2 | 3 | 4 | 5 |
---|---|---|---|---|---|---|
Player’s gain (\$) | \(-4\) | \(-3\) | \(-1\) | 0 | 1 | 4 |
(b) Determine whether this game is fair. Justify your answer. [3]
▶️Answer/Explanation
Markscheme
(a)
Sum of probabilities equals 1:
\(0.15+0.20+k+0.16+2k+0.25=1 \;\Rightarrow\; 0.76+3k=1 \Rightarrow \boxed{k=0.08}.\) M1 A1
\(0.15+0.20+k+0.16+2k+0.25=1 \;\Rightarrow\; 0.76+3k=1 \Rightarrow \boxed{k=0.08}.\) M1 A1
(b)
With \(k=0.08\), expected gain: \[ E(G)=(-4)(0.15)+(-3)(0.20)+(-1)(0.08)+(0)(0.16)+(1)(0.16)+(4)(0.25). \] Compute: \(-0.60-0.60-0.08+0+0.16+1.00=\boxed{-0.12}.\) M1 A1
Since \(E(G)\neq 0\) (negative), the game is not fair. R1
Since \(E(G)\neq 0\) (negative), the game is not fair. R1
Total Marks: 5