(a)[3]
Find the standard deviation for the lengths.
(b)[3]
Find the probability that fewer than 3 of these rolls have lengths more than $77\,\text{m}$.
Mathematics 9709 · AS & A Level · Continuous random variables
Continuous random variables — practice question
Roll lengths of parcel tape are normally distributed with mean $75\,\text{m}$, and $15\%$ of the rolls are shorter than $73\,\text{m}$. Alison purchases 8 rolls of parcel tape.
Worked solution & mark scheme
This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “With $x=73$, use $z = \dfrac{73-75}{\sigma}$ and take $\sigma = 1.93$” …
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