Question

	None Used	Only Facebook, not Snapchat	Only Snapchat, not Facebook	Both Facebook and Snapchat	Total
Female	6	4	4	12	26
Male	4	5	7	8	24
Total	10	9	11	20	50

• Use a normal approximation to the binomial distribution (with mean and std. dev. calculated based on your data) and compute the following:
• 1. in a sample of 40, the probability that exactly 19 say they have used both Facebook and Snapchat.   
• Don’t forget to correct for continuity!!

Answer 1

Observe that the number of people who use both Facebook and Snapchat in our given sample is 20. Hence the proportion of people who use both Facebook and Snapchat is 20/50 = 0.4. Hence by our Normal Approximation based on this sample, if X is the number of people who use both Facebook and Snapchat out of 40 people, then

Hence the probability that in a sample of 40, exactly 19 say they have used both Facebook and Snapchat is