posted by sarah on .
find the standard deviation for the following: 8,5, 12, 8, 9, 15, 21, 16, 3. There is a formula but our teacher wants us to do it a specific way.
For example, 47, 41, 32, 53, 57. First you find the mean, which is 46 and then subtract it with each number in the set so you get 1, -5, -14, 7, 11. then you square each # to get 1, 25, 196, 49, 121. then add all the numbers to get 392 & you do 392/n-1 (n being how many #s there are in the set) so 392/5-1 = 98 then you square root 98 & the standard deviation is 9.9.
For 8, 5, 12, 8, 9, 15, 21, 16, 3 the standard deviation is 5.73973 but when i tried the process i get a completely different answer. First the i found the mean, which is 10.77777778. (97/9) but after this i started messing up, help? Can't use the formula!
if you have a graphing calculator, go to catalog (normally you can get there by hitting the 2nd button than 0), then hit the alpha button and hit T then scroll up to stdDev which is standard deviation, hit enter, then type in the bracket (to get to is 2nd button then parantheses), type in the numbers you need with a comma in between each number, end the bracket AND end the parantheses then hit enter and there's your answer. always trust a calculator more than written out because of the issue of human error