Question

5. GMAT scores are approximately normally distributed with a mean of 547 and a standard deviation of 95. Estimate the percentage of scores that were(a) between 357 and 737. %(b) above 737. %(c) below 452. %(d) between 452 and 737. %

Answer 1

Problem Statement

The question tells us that the GMAT scores are approximately normally distributed with a mean of 547 and a standard deviation of 95.

We are asked to find the percentage of scores that were:

a) between 357 and 737.

b) above 737

c) below 452

d) between 452 and 737.

Solution

a) Between 357 and 737:

`\begin{gathered} 357\text{ is 2 standard deviations less than the mean of 547. That is,} \\ 547-2(95)=357 \\ \text{This means that 357 is }(95)/(2)\text{ \% from the mean}=47.5\text{ \% from 547.} \\ \\ 737\text{ is 2 standard deviations greater than the mean of 547. That is,} \\ 737-2(95)=547. \\ \text{This means that 737 is }(95)/(2)\text{ \% from the mean }=47.5\text{ \% from 547} \\ \\ \text{Thus the range 'Between 357 and 737' is:} \\ (47.5+47.5)\text{ \%}=95\text{ \%} \end{gathered}`

b) Above 737

`\begin{gathered} 737\text{ is 2 standard deviations away from the mean as shown in question A.} \\ \text{Thus, the percentage of scores above 737 must be:} \\ 100\text{ \% - (50 + 47.5)\% }=2.5\text{ \%} \end{gathered}`

c) Below 452:

`\begin{gathered} 452\text{ is 1 standard deviation from the mean.} \\ \text{Thus the percentage of scores below 452 must be:} \\ 50\text{ \% - 34\% = 16\%} \end{gathered}`

d) Between 452 and 737: