Calculating STD quickly Math Destroyer

ChewyDrop

2+ Year Member
Practice 1: #39

Which of the following best represents the standard deviation of the data set {3,4,5,6,7}

Solution:
Subtracting 5 from each of the data points we get the set {-2,-1,0,1,2}. Squaring each of these values, taking their sum, and dividing by 5 gives us the variance.

My question is the number "5" that is being subtracted and divided the mean or the total data values in the set?

8_man

Achievement Unlocked: Dental School
2+ Year Member
On the actual DAT, just make an educated guess. The mean is clearly 5, while the differences range from + or - 1 and 2. So... I'd probably say 1.5?

Answer choices on the actual DAT tend to be spaced out generously, so you can tell right away.

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8_man

Achievement Unlocked: Dental School
2+ Year Member
But for your information... The 5 you subtract with is from the mean. The 5 you divide with is from the number of terms in the set.

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orgoman22

DAT DESTROYER... Dr. Romano and Nancy
Vendor
10+ Year Member
Practice 1: #39

Which of the following best represents the standard deviation of the data set {3,4,5,6,7}

Solution:
Subtracting 5 from each of the data points we get the set {-2,-1,0,1,2}. Squaring each of these values, taking their sum, and dividing by 5 gives us the variance.

My question is the number "5" that is being subtracted and divided the mean or the total data values in the set?
You subtract each number from the mean which is 5 ,
square each difference then you add and you divide by the number of items which also happens to be 5.

Then you take the square root to get the standard deviation. Hope this helps