O-LevelMathematicsProbability4024/21 · Oct/Nov 2025 · Q177 Marks
The table shows the times taken by 80 people to complete a race. [Table with Time (t minutes) and Frequency]
- (a)Calculate an estimate of the mean time taken to complete the race.[4]
- (b)Two of the 80 people are selected at random. Find the probability that one takes 30 minutes or less and the other takes more than 60 minutes to complete the race.[3]
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Mark scheme
Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.
- 17(a) 43.875 oe [4] M1 for correct midpoints soi M1 for use of Efx where x is in the correct interval including boundaries M1 (dep on 2nd M1) for Efx ÷ 80
- 17(b) 5/158 oe [3] M2 for [2 × ] (20/80 × 5/79) oe or M1 for (20/80 or 5/80) or (5/79 or 20/79) seen If M0, SC1 for answer 1/32 oe
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