I know how to calculate question which are phrased like so
A study of data collected at a company manufacturing flashlight batteries shows that a batch of 8000 batteries have a mean life of 250 minutes with a standard deviation of 20 minutes. Assuming a Normal Distribution, estimate:
(i) How many batteries will fail before 220 minutes?
Answer = 534.4
But I can not figure questions phrased like this:
Support call times at a technical support center are Normally distributed with a mean time of 8 minutes and 45 seconds and a standard deviation of 1 minute and 5 seconds. On a particular day, a total of 500 calls are taken at the centre. How many of these calls are likely to last more than 10 minutes
I dont understand how to find the z-score in this question as its to do with time?