Question

[Statistics] Someone samples 15 people and gets a sample mean of 115.2 minutes with a standard deviation of 10 minutes. What sample size is needed if the margin of error of the 90% confidence interval is to be no more than 4 minutes?

Answer 1

So I set up the equation
1.645 = (113.2-115.2)/(10/sqrt(N)) (since we don't know the t value yet I'm guestimating with the z score).
But that leaves me with N = 64, which is way out of line with the options of 6,17,26,30. So I'm a bit confused.