A certain characteristic in a large population has a distribution that is symmetric about the mean m. If 36 percent of the distribution lies within one standard deviation d of the mean, what percent of the distribution is less than m + d ? Choose the correct choice from the following options: A) 16% B) 32% C) 68% D) 84% E) 92%
This is easiest to solve with a bell-curve histogram. m here is equal to µ in the Gaussian normal distribution and thus m = 50% of the total population.   So, if 36% is one st.Dev, then on either side of m we have  36/2= 
<gadget id="calculator"> 36/2</gadget>
<output>18</output>
18%. So,18% are to the right and left of m (= 50%). In other words, our value m + d = 50 + 18= 
<gadget id="calculator">50 + 18</gadget>
<output>68</output>
68% goingfrom the mean m, to the right of the distributionin the bell shaped histogram.. This means that 68% of the values are below m + d.   Like I said, doing it on a bell-curve histogram is much easier to fullygethow this works, or you could apply GMAT percentile jargon/theory to it   68%
<result>C</result>
A certain characteristic in a large population has a distribution that is symmetric about the mean m. If 36 percent of the distribution lies within one standard deviation d of the mean, what percent of the distribution is less than m + d ?