(i)[3]
90% of Moses's phone calls last more than $t$ minutes. Find the value of $t$.
(ii)[5]
Find the probability that, in a random sample of 9 phone calls made by Moses, more than 7 have a duration that is within 1 standard deviation of the mean.
Mathematics 9709 · AS & A Level · Continuous random variables
Continuous random variables — practice question
The length of each phone call Moses makes has a normal distribution with mean 6.5 minutes and standard deviation 1.76 minutes.