A Bell Curve (Normal Distribution) has a mean of − 1

Brent@GMATPrepNow wrote:A little extra background on standard deviations above and below the mean

If, for example, a set has a standard deviation of 4, then:
1 standard deviation = 4
2 standard deviations = 8
3 standard deviations = 12
1.5 standard deviations = 6
0.25 standard deviations = 1
etc


So, if the mean of a set is 9, and the standard deviation is 4, then:
2 standard deviations ABOVE the mean = 17 [since 9 + 2(4) = 17]
1.5 standard deviations BELOW the mean = 3 [since 9 - 1.5(4) = 3]
3 standard deviations ABOVE the mean = 21 [since 9 + 3(4) = 21]
etc.

In the stated questions, we're asked to find values that are within 3 standard deviations of the mean
So, as David has demonstrated, we need to determine 3 standard deviations above the mean AND 3 standard deviations below the mean

Cheers,
Brent

jain2016 wrote: Hi Brent ,

3 Standard deviation above the mean = -5/8 [since -1 + 3/8 = -5/8]

3 standard deviation below the mean = -11/8 [since -1 - 3/8 = -11/8]

Now what will be the next step?

Please advise.

Many thanks in advance.

SJ