(a)[2]
Determine the probability that a person selected at random from this town watches television for fewer than $21$ hours in a week.
(b)[3]
Determine $k$ so that $\text{P}(X < k) = 0.75$.
Mathematics 9709 · AS & A Level · The normal distribution
The normal distribution — practice question
For one town, the weekly television-watching time, $X$ hours, is normally distributed with mean $15.8$ hours and standard deviation $4.2$ hours.
Worked solution & mark scheme
This 5-mark question has a full step-by-step worked solution and mark scheme. One marking point: “After standardising, $P(X<21)=P\! \left(Z<\dfrac{21-15.8}{4.2}\right)=\Phi(1.238)$.” …
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