How to calculate variance QR problem #37 on 2007 ADA

[Bobby Fischer]

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I have no clue on this one. Ideas? Internet is only mudding up the waters. Best guess at this point is that there are various methods and I don't know which one the DAT is going to use?

 

[jpower100]

I know what you mean bud so i'm going to summarize the one and only formula you need to know for variance and standard deviation for the DAT for ya.

1. Calculate the mean
2. Calculate the difference between each term and the previously calculated mean
3. Square them
4. Divide by the number of the terms

Now what you have is the variance. If you want the standard deviation, you just square root it.

This is definitely an important topic as I have seen it myself on the real DAT today morning haha.

 

[Bobby Fischer]

I know what you mean bud so i'm going to summarize the one and only formula you need to know for variance and standard deviation for the DAT for ya.

1. Calculate the mean
2. Calculate the difference between each term and the previously calculated mean
3. Square them
4. Divide by the number of the terms

Now what you have is the variance. If you want the standard deviation, you just square root it.

This is definitely an important topic as I have seen it myself on the real DAT today morning haha.

Okay, lets see if I can get it here:

"The numbers (1, 2, 3, 6) have an average (arithmetic mean) of 3 and a variance of 3.5. What is the average (arithmetic mean) and variance of the set of numbers (3, 6, 9, 18)?

A. 9, 31.5

B. 3, 10.5

C. 3, 31.5

D. 6, 7.5

E. 9, 27.5"




step 1: calculate mean. =9

step 2: difference between mean and each given number =6,3,0,9

step 3: square differences =36,9,0,81

step 4: calc sum =126

step 5: divide sum by number of givens =31.5!!
Awesome. Thanks for the help!

 

[ktran17]

variance is the (standard deviation)^2

source: math destroyer notes