Question

A manufacturer of batteries knows that 10% of the batteries produced by a particular production line are defective. A sample of 200 batteries is removed for testing.
a) What is the probability that exactly 20 batteries in the sample are defective?
[2 marks]
b) What is the probability that at least 20 batteries in the sample are defective?
[7 marks]

Answer 1

I think you need only an answer without expanation so let's start.
a) $P = \frac{200!}{180!x20!} * 0,1^{20}*0,9^{180} = 0.093636$
b) $Probability = 0.5 + \frac{1}{2} (0.093636) = 0.54682$