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5) *The number of major earthquakes in a year is approximately normally distributed with a mean of 20.8 and a standard deviation of 4.5.
a) Find the probability that in a given year there will be less than 21 major earthquakes.
b) Find the probability that in a given year there will be between 18 and 23 major earthquakes.
a) Z=21-20.8/4.5 Z=0.04 P=0.5160
b) Z= 18-20.8/4.5 Z= -0.62 P= 0.2676
Z= 23-20.8/4.5 Z=0.488 P= 0.6844
0.68-0.26= 0.42
Vivian Gomez has for b) 0.42. Professor Halleck has 0.4203. I have 0.6844-0.2676=0.4168
Which one is right?
if it helps I also got 0.4203. For P( x>18) I got a z score of -0.62 which gets me to a P value of 0.2676 and for P(x<23) I got a z score of 0.49 which gets me to a P value of 0.6879. Then you do 0.6789 minus 0.2676 and you get 0 .4203 ( which is about 42%)
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