A-LevelMathematicsProbability and statistics9709/52 · Oct/Nov 2025 · Q13 Marks
A coin is biased so that the probability of obtaining a head when it is thrown is 0.4. The coin is thrown repeatedly until the first head is obtained.
- (a)Find the probability that the first head is obtained on the 5th throw.[1]
- (b)Find the probability that the first head is obtained after the 6th throw.[2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.
- [B1] CAO.
- [M1] 0.6^k, k = 5,6,7. Or 1 - (0.4+0.4×0.6+0.4×0.6^2 +0.4×0.6^3 +0.4×0.6^4 + 0.4×0.6^5) The blue terms may be omitted or included. Condone omission of final bracket only. Condone omission of both brackets if recovered by 1 – 0.953344... or final answer 0.046656 rounded to at least 4SF.
- [A1] 0.046656 rounded to at least 3SF.
Write your answer and get it marked
On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.
Sign up free →