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looks tricky! but simple

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Junior | Next Rank: 30 Posts
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by desiguy » Tue Jul 22, 2008 4:28 am
for a certain examination a score of 58 was 2 standard deviations below the mean and a score of 98 is 3 standard deviations above the mean. what was the mean score ?

74,76, 78, 80,82

Please solve
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by sudhir3127 » Tue Jul 22, 2008 4:41 am
Let M = mean
Let SD = stand deviation

M + 3SD = 98
M - 2SD = 58

solve it

5SD = 40
SD = 8


M - 2(8) = 58
M = 58 + 16
M = 74


hope it helps...
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by newera » Tue Jul 22, 2008 4:47 am
OA is 74.

This is very simple, so don't worry.

Basically you want to figure out how many units is included in one standard deviation. So take your highest number 98 substract the lowest value from it. 98-58=40. Divide this by the total number of standard deviations. 40/5=8.

Now we know that one std deviation has 8 units. As such, we can figure out the mean.

58 is 2 std dev away from the mean --> 58 + 2(8)=74

98 is 3 std dev above the mean --> 98 - 3(8)=74
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