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2.4.4 Mean and variance of the binomial (A-level only)

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Question 11

A botanical garden offers a "rare bloom" seed in 15% of its wildflower packets. No packet contains more than one rare bloom seed. Packets are sold in wholesale bundles of 12.

a.

(i) Suggest a suitable distribution to model the number of rare bloom seeds, SSS, found in a single bundle. (ii) State one necessary assumption for this model to be valid.

[2]
b.

Calculate the probability that out of 3 randomly selected bundles, exactly 1 bundle contains exactly 2 rare bloom seeds.

[3]
c.

Determine the probability that a randomly selected bundle contains at least 3 rare bloom seeds.

[2]
d.

A regional distributor buys 120 bundles for a seasonal sale.

Using a normal approximation, find the probability that fewer than 25 of these bundles contain at least 3 rare bloom seeds.

[4]

2.4.4 Mean and variance of the binomial (A-level only) Questions

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