I've attached the question.
μ=np and σ=√(np(1-p))
Im using the normal distribution function on my calculator to avoid using z tables
The Attempt at a Solution
The mean I calculated it to be 160/4 = 40. standard deviation sqrt(160*1/4*3/4)=5.47723
The question is asking for at least 40(greater or equal to 40) that will choose biscuits but because this is a normal distribution it will be the same as greater than 40 so if I use an X value of 40 the probabilities should just equal 0.5000 right? however the answer is 0.5364