vigneshpandi wrote:

The lifetime of all the batteries produced by a certain company in a year have a distribution that is symmetric about the mean m. If the distribution has a standard deviation of d, what percent of the distribution is greater than m+d?

(1) 68 percent of the distribution lies in the interval from m-d to m+d, inclusive

(2) 16 percent of the distribution is less than m-d

Can sum1 explain the concept behind this...Looking at the answer I have come up with my own assumptions...

The answer is D

Statement 1) (1) 68 percent of the distribution lies in the interval from m-d to m+d, inclusive

Standard deviation is a bell curve with m at the centre and +d on the right and -d not the left. (But remember standard deviation in itself can never be negative)

Also remember the graph of Standard deviation is the most symmetric graph that you will see in mathematics. It also has some unique properties related to (mean + deviation) and (mean + 2 * deviation) and so on

but for this question this much info is enough.

Therefore if you assume m to be at point 0 then m+d=34% and m-d= 34 %

we want to know the value of m+d ; SUFFICIENT

2) 16 percent of the distribution is less than m-d

Since 16 % of distribution is less than m-d therefore 16 % of the distribution will be more than m+d ; a totalof 32% of 100 leaving 68% to be distributed equally into

m+d and m-d

therefore both m+d and m-d will be 68/2 = 34

Sufficient

Answer is D

_________________

Posting an answer without an explanation is "GOD COMPLEX". The world doesn't need any more gods. Please explain you answers properly.

FINAL GOODBYE :- 17th SEPTEMBER 2016. .. 16 March 2017 - I am back but for all purposes please consider me semi-retired.