Question

Let X be normal with mean 80 and variance 9. Find P(X < 81) and P(78 < X < 82) Let X be normal with mean 80 and variance 9. Find P(X < 81) and P(78 < X < 82) @Mathematics

Answer 1

P(x<81) = P (z<1/3) =.6293 from the z tables

Answer 2

z= 81-80/3 =1/3

Answer 3

P(78<x<82) = P(x<82) - P(x<78)

Answer 4

P(x<82) = P(z<2/3) = 0.7486

Answer 5

P(x<78)=P(Z<-2/3) = 1 - .7486 =.2514

Answer 6

so P(78<x<82) = .7486-.2514 = .4972

Answer 7

hope that helps

Answer 8

I understand the last part, but for the first part, according to the book, it gives an answer of 0.6306. I think it may be wrong, but I am inclined to think it may be wrong

Answer 9

hmm may be wrong on the book

Answer 10

or they have estimated between the z values I used 1/3 = 0.33 they may have been more acurate using0.333333333333 etc

Answer 11

or used the graphing calculator

Answer 12

perhaps. it also says the value for the other problem is 0.4950. so they have gotten different values as well for that. i don't know

Answer 13

using the Ti83 calculator and nomalcdf(-1E99, 81, 80, 3) = 0.6305

Answer 14

It's just rounding error

Answer 15

nomalcdf(78, 82, 80, 3) =0.4950

Answer 16

so they must be using technology to get the answer and not the tables

Answer 17

you may be right. thanks though, to the both of you, for your answer. at least i know my answer was not off.