If the sum of 10 observations is 12 and the sum of their squares is 18, then the standard deviation is: 

This question was previously asked in
SSC CGL Tier-II (JSO) 2022 Official Paper (Held On: 4 March 2023)
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  1. 4/5
  2. 2/5
  3. 3/5
  4. 1/5

Answer (Detailed Solution Below)

Option 3 : 3/5
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SSC CGL Tier 1 2025 Full Test - 01
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The correct answer is 3/5
Key Points

Standard deviation =  
Therefore, Variance V(X) = 
or, 


Given, the sum of 10 observations is 12 and the sum of their squares is 18. 
Thus, n = 10,  
Therefore, mean
Plugging this information into the equation of variance V(X), we have

= 1.8 - 1.44

=0.36
Hence, the required standard deviation 

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