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A community center recorded the number of evening workshops it held in each of the 12 months of last year. What was the standard deviation of the number of evening workshops held per month last year?
(1) The standard deviation of the numbers of evening workshops held per month during the first 6 months of last year was 1.
(2) The standard deviation of the numbers of evening workshops held per month during the last 6 months of last year was 5.
The OA will be automatically revealed on Tuesday 12th of May 2026 07:00:38 PM Pacific Time Zone
(1) The standard deviation of the numbers of evening workshops held per month during the first 6 months of last year was 1.
(2) The standard deviation of the numbers of evening workshops held per month during the last 6 months of last year was 5.
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The OA will be automatically revealed on Tuesday 12th of May 2026 07:00:38 PM Pacific Time Zone
07 May 2026, 20:40
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We need the standard deviation for all 12 months.
Statement (1):
First 6 months have standard deviation 1.
This gives information only about half the data. We do not know the last 6 months or the overall distribution.
Not sufficient.
Statement (2):
Last 6 months have standard deviation 5.
Again, only partial information.
Not sufficient.
Together:
Knowing the standard deviations of the two halves still does not determine the standard deviation of all 12 months, because the two groups could have very different means.
Example:
Different overall SDs are possible.
Answer: E
Statement (1):
First 6 months have standard deviation 1.
This gives information only about half the data. We do not know the last 6 months or the overall distribution.
Not sufficient.
Statement (2):
Last 6 months have standard deviation 5.
Again, only partial information.
Not sufficient.
Together:
Knowing the standard deviations of the two halves still does not determine the standard deviation of all 12 months, because the two groups could have very different means.
Example:
- First 6 months: all centered near 10
- Last 6 months: all centered near 100
Different overall SDs are possible.
Answer: E
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08 May 2026, 09:09
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(1)
First 6 months have a standard deviation of 1
No information about the last 6 months or relationship between the two groups.
Insufficient
(2)
Last 6 months have a standard deviation of 5.
No information about the first 6 months or relationship between the groups.
Insufficient
(1) + (2)
The standard deviation of a combined set depends not just on the SD of the individual groups but also on how far apart their averages are. For example:
Scenario A: Both groups have a mean of 10. The combined SD will be relatively low.
Scenario B: The first group has a mean of 10 and the second group has a mean of 1,000. Even if the internal SDs are 1 and 5, the combined SD will be massive because the data points are extremely far apart.
Since we don't know the means, we cannot determine a single value for the 12-month SD.
Insufficient
Answer: E
First 6 months have a standard deviation of 1
No information about the last 6 months or relationship between the two groups.
Insufficient
(2)
Last 6 months have a standard deviation of 5.
No information about the first 6 months or relationship between the groups.
Insufficient
(1) + (2)
The standard deviation of a combined set depends not just on the SD of the individual groups but also on how far apart their averages are. For example:
Scenario A: Both groups have a mean of 10. The combined SD will be relatively low.
Scenario B: The first group has a mean of 10 and the second group has a mean of 1,000. Even if the internal SDs are 1 and 5, the combined SD will be massive because the data points are extremely far apart.
Since we don't know the means, we cannot determine a single value for the 12-month SD.
Insufficient
Answer: E
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