How many students would you expect to wait more than 18.5 minutes?

Question

200 senior high students were asked how long they had to wait in the cafeteria line for lunch. Their responses were found to be normally distributed, with a mean of 15 minutes and a standard deviation of 3.5 minutes.



How many students would you expect to wait more than 18.5 minutes?

Answer 1

Looking at the Bell Distribution curve, the region that includes the mean and standard deviation comprises nearly 68.3% of the total data points which is the number of students. The rest is the students who will wait less than 11.5 minutes and greater than 18.5 minutes constitute 100%-68.3% = 31.7%. Therefore the number of students that are expected to wait more than 18.5 minutes = 31.7%/2=15.85%

 

That is (15.85/100)x200students = 31.7 say 32 students