Normal Distribution Math Example 4

Solution

1. 1
   $400$ is $1$ standard deviation below the mean, and $700$ is $2$ standard deviations above the mean.
2. 2
   By the empirical rule, the area from $-1\sigma$ to $+1\sigma$ is about $68\%$.
3. 3
   The area from $+1\sigma$ to $+2\sigma$ is about $13.5\%$.
4. 4
   Add them: $68\% + 13.5\% = 81.5\%$.