The times it takes 5th graders to complete a mathematics problem are Normally distributed with mean 2 min and standard deviation 0.8 min. What is the probability that a randomly chosen 5th grader will take more than 2.5 minutes to complete the problem?

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Answer 1 · 2017-04-08T09:51:13

0.266

X ~ N(2, #0.8^2#)

P (X > 2.5)

= P #(Z > (2.5-2)/0.8)#

= P #(Z > 0.625)#

= 1 - #Phi (0.625)#

= 1 - 0.734

= 0.266