Thread: Finding X Given Normal Probability

Hello everyone,

I have a question on a normal distribution problem where I have to find X given a certain probability. I know how to do it, but it seems like the method I used to achieve the answer is incorrect, and I don't understand why. I hope you guys can point me to the right direction



I have posted an image with the problem above and my way of solving it vs. professor's way.


What I'm confused about: Why is this a left hand tail problem instead of a right hand tail like my way of doing it? Does the problem give out a hint stating that it's a left hand tail?

98% last longer than X hours, therefore only 2% have a shorter life.
The way you have done it is the opposite way around i.e.only 2% last longer than X hours, therefore 98% have a shorter life.

Originally Posted by pickslides

98% last longer than X hours, therefore only 2% have a shorter life.
The way you have done it is the opposite way around i.e.only 2% last longer than X hours, therefore 98% have a shorter life.

How do i know if it's left hand tail or a right hand tail?