A certain characteristic in a large population has a distribution that is symmetric about the mean m. If 64 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 choices
A) 16% B) 32% C) 48% D) 82% 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 64% is one st.Dev, then on either side of m we have  64/2= 
<gadget id="calculator"> 64/2</gadget>
<output>32</output>
32%. So, 32% are to the right and left of m (= 50%). In other words, our value m + d = 50 + 32= 
<gadget id="calculator">50 + 32</gadget>
<output>82</output>
82% goingfrom the mean m, to the right of the distributionin the bell shaped histogram.. This means that 82% 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   82%
<result>D</result>
A certain characteristic in a large population has a distribution that is symmetric about the mean m. If 64 percent of the distribution lies within one standard deviation d of the mean, what percent of the distribution is less than m + d ?