Question

Find the range and the standard deviation of the following prices of backpacks: $11.99, $8.84, $16.98, $9.99, $10.45, $10.86, $11.99.
Okay I know the range is highest value - lowest value which is $16.98-$8.84=$8.14
How do I figure out the standard deviation?

Answer 1

there is an approximation rule for sd as being 1/4 of the range

Answer 2

there are more precise methods tho that take alot longer to determine tho

Answer 3

The standard deviation is the square root of the variance.
The variance is the expected value of (the price squared) minus the (expected value of the price) squared.

So 1.) square each of the prices and find the average.
Then 2.) find the average price and square it.
Then subtract the second from the first.

The square root of that is the Standard Deviation.

Answer 4

your step one seems off to me

Answer 5

ok let me try it thanks

Answer 6

step 1 find average

step 2 find the difference between each data point and the average

step 3 square each result

step 4 add the squares up

step 5 divide by the number of data points if its a population; or n-1 if its a sample

step 6 sqrt that value

Answer 7

i recall there being a different method tho, but i can never recall it. they say its easier tho

Answer 8

amistre64 is not incorrect, but my method is the easier method. For "Sample Standard Deviation" you would instead of finding the average, you would divide by n-1.

Answer 9

@amistre64 yeah i have that formula, but the average is 11.6 and when i do step 2 the difference between the data and the average is incorrect, and I don't know why?

Answer 10

i have to wonder if your solution is spose to use the approximate fromteh range, or the accurate from the formulas ....

Answer 11

hmmm im not sure

Answer 12

$8.14/4 = 2.035 as an approximate

the wolf gives me the accurate as: 2.624 ; which is prolly for a population

Answer 13

ok im still working it out and it seems pretty close thank you

Answer 14

youre welcome; the decimals make it a pain to me :)