A-LevelMathematicsProbability and statistics9709/51 · Oct/Nov 2025 · Q24 Marks
A fair six-sided dice with faces labelled 1, 2, 3, 4, 5, 6 is thrown repeatedly until a 6 is obtained.
- (a)Find the probability that a 6 is obtained for the first time on the 8th throw.[1]
- (b)Find the probability that a 6 is obtained for the third time on the 7th throw.[3]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.
- [B1] Accept 0.0465136... rounded to 3 or more SF. Accept 78125/1679616.
- [B1] (5/6)^4 * (1/6)^3 * xd, d>=1.
- [M1] p^r(1-p)^(n-r) x nCr, 0<p<1, accept nPr/r!.
- [A1] AWRT. 3125/93312, 9375/279936.
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