- #1

- 134

- 12

## Homework Statement

A student sits a test and is told that the marks follow a normal distribution with mean 100. The student receives a mark of 124 and is told that he is at the 68th percentile. Calculate the variance of the distribution.

## Homework Equations

https://lh3.googleusercontent.com/proxy/XW4iFBVEU-T7v_I-U5zV6mo7CvCYxVfS6kbEiAuBBsiEcJWb-P7AHpF6ciRBv4skZW5pqDilEHh9F5zdeCfu0N0ztdfDS_lm-A=w685-h215-nc

## The Attempt at a Solution

I replaced 0.68 for f (x) and 100 for μ and 124 for x. I tried to rearange to solve for σ but was unsuccessful only getting as far as,

0.553 = -288/σ^2 - lnσ

I think my approach might be completely wrong, or is there a way of doing this with the aid of a graphic calculator?