The times taken, in minutes, for trains to travel between Alphaton and Beeton are normally distributed with mean 140 and standard deviation 12.
- (i)Find the probability that a randomly chosen train will take less than 132 minutes to travel between Alphaton and Beeton.[3]
- (ii)The probability that a randomly chosen train takes more than k minutes to travel between Alphaton and Beeton is 0.675. Find the value of k.[3]
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2019). The mark or mark type is shown in brackets.
- [M1] Using ± standardisation formula, no continuity correction, not σ² or √σ
- [M1] Appropriate area Φ from standardisation formula P(z<....) in final solution
- [A1] Condone linear interpolation = 0.25243
- [B1] ±0.454 seen
- [M1] An equation using the standardisation formula with a z-value (not 1 – z), condone σ² or √σ
- [A1] B0M1A1 max from -0.45
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