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Standard Deviation

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by bburton11 » Fri Jun 12, 2009 6:47 am
For a certain examination, a score of 58 was 2 standard deviation below the mean, and a score of 98 was 3 standard deviation above the mean. What was the mean score for the examination?

74

*I don’t know why standard deviation is such a problem for me
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by scoobydooby » Fri Jun 12, 2009 6:53 am
98=M+3SD..............1
58=M-2SD...............2

subtracting 2 from 1 we get 40=5SD=> SD=8

replacing in either 1 or 2 we get M=74
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by ssmiles08 » Fri Jun 12, 2009 7:17 am
you know another helpful way is just draw out a small diagram:

58 (2)---(1)---(0)----(1)----(2)----(3) 98

total distance is 5 std. deviations

so its 98 - 58 = 40

40/5 = 8.

each st. dev is 8 units apart. We also know (0) is the mean. so 58 + 16 = 74
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by gauravkhare » Fri Jun 12, 2009 11:36 am
you know another helpful way is just draw out a small diagram:

58 (2)---(1)---(0)----(1)----(2)----(3) 98

total distance is 5 std. deviations

so its 98 - 58 = 40

40/5 = 8.

each st. dev is 8 units apart. We also know (0) is the mean. so 58 + 16 = 74

GOOD ONE!!!!
gaurav
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