Help with a statistics problem?

Question

Meteorologists have been recording the daily maximum temperature in Glendale since 1874. The population mean is 62 degrees, with a population standard deviation of 15 degrees. New federal regulations say that towns should prepare for extreme weather. That is, when the daily maximum temperature is less than 30 degrees or more than 90 degrees. How many days each year(assuming it is not a leap year) should Glendale expect to have extreme weather?

A) about 15-16 days
B) about 17-18 days
C) about 20-21 days
D) about 22-23 days

I got this wrong on a test and have to correct it. Please help

Answer 1

How did you try to do it?

You want to find
P(T<30) + P(T>90)

This probability times 365 days/year gives the number of days in the year for extreme weather.

You'll need to convert those 30 and 90 deg into standard Z varibles for use with a table.

And recall that
P(T>90) = 1-P(T<90)