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Jonathan's score

by sanju09 » Wed May 19, 2010 4:31 am
The exam scores of all 500 students were recorded and it was determined that these scores were normally distributed. If Jonathan's score is 0.8 standard deviation above the mean, then how many, to the nearest unit, students scored above Jonathan?
(A) 106
(B) 160
(C) 250
(D) 394
(E) 400
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by clock60 » Wed May 19, 2010 1:12 pm
sanju09 wrote:The exam scores of all 500 students were recorded and it was determined that these scores were normally distributed. If Jonathan's score is 0.8 standard deviation above the mean, then how many, to the nearest unit, students scored above Jonathan?
(A) 106
(B) 160
(C) 250
(D) 394
(E) 400
pretty weak in such problems, only want to try
if Jonatan`s score lies within 1 SD, then 68% of 500=340 students have th same score ( i mean within 1 SD, mean+/-SD)
then we left with 500-340=160 students whose score lies within 2, or 3 SD, (mean+/-2*SD)
as we are interested only in those who score above Jonatan,ie (mean+2SD)-95,4% and (mean+3SD)-99.7% the anser will be less that 160 and the only option is 106
so my answer-A
is it right?
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