A-LevelMathematicsProbability and statistics9709/51 · Oct/Nov 2025 · Q16 Marks
The random variable X takes the value x with probability kx², where k is a constant and x takes the values -2, 1, 2, 3 only.
- (a)Draw up the probability distribution table for X, giving the probabilities as numerical fractions.[3]
- (b)Find E(X).[1]
- (c)Find P(X ≠ 2|X > 0).[2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.
- [B1] Using sum of probabilities =1 to form an equation in k or value of k stated.
- [B1] Table with at least 2 correctly linked probabilities accurate. May be in terms of k.
- [B1] 4 correctly linked probabilities accurate. May not be in a table.
- [B1FT] FT 28 × their k or correct with 0<p<1.
- [M1] their P(1)+P(3) / their P(1)+P(2)+P(3). May be in terms of k. With 0<p<1.
- [A1] CAO. If table correct, accept 10/18 / 14/18 or 5/9 / 7/9.
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