During the previous year, an online store sold a large number of computers. $55\%$ of these computers were made by company $F$, $30\%$ by company $G$ and $15\%$ by company $H$. A random sample of $3$ customers, each of whom bought a computer from this store, is selected.
(a)[1]
Find the probability that the $3$ customers bought computers made by three different companies.
(b)[3]
A random sample of $12$ customers, each of whom bought a computer from this store, is selected. Find the probability that fewer than $10$ of these customers bought a computer made by company $F$.
(c)[5]
A random sample of $140$ customers, each of whom bought a computer from this store, is selected. Use a suitable approximation to find the probability that more than $24$ of these customers bought a computer made by company $H$.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Correctly evaluate $0.55\times0.3\times0.15\times3=0.1485=\frac{297}{2000}$.” …