Wendy's journey to work consists of three parts: walking to the train station, riding on the train and then walking to the office. The times, in minutes, for the three parts of her journey are independent and have the distributions $$\(\mathrm{N}\left(15.0,1.1^{2}\right), \mathrm{N}\left(32.0,3.5^{2}\right)\)$$ and $$\(\mathrm{N}\left(8.6,1.2^{2}\right)\)$$ respectively. If Wendy's journey takes more than 60 minutes, she is late for work. Find the probability that, on a randomly chosen day, Wendy will be late for work. ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................

Mathematics
IGCSE&ALevel
CAIE
Exam No:9709_s21_qp_62 Year:2021 Question No:4(b)

Answer:

\(\frac{60-" 55.6 "}{\sqrt{" 14.9 "}}[=1.140]\)
\(1-\phi(" 1.140 ")\)
\(0.127(3 \mathrm{sf})\)

Knowledge points:

6.2.1.5 if X and Y have independent normal distributions then aX + bY has a normal distribution

Solution:

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