Maths S1 using calc for mean and s.d.

[Mortal9090]

Hi,

I have confusion on using calc to solve simple mean and s.d. questions for example a raw data have been given e.g
1,2,3,41,31,55,32,45,73,12 etc

if the question asks for what the mean is, should we write them all with sum and divide with 'n' and so on to show the working or just simply using it via calculator and writing answer would be sufficient

similarly, if we talk about s.d. (which requires little work) sqrt((sum(x^2)/n)-mean(x)) formula, should we write all the items individually, square them, add them, show complete working in order to show the required s.d.

or we can simply use calculator and write the s.d.? (usually a question with finding sd and mean gives you only 2 marks)

 

[Amna]

depends on the number of marks, really, but i think if it's 2 marks just the formula, and the correct answer ought to work. however, it's always good to show the working, there's less chance of messing up, and more marks for the working seen in case u do mess up. personally, i usually copy the formula from MF9, substitute the values, give the answer.

 

[ahmed t]

well u can write ur value in of sum(x^2) instead of writing every value.

 

[Mortal9090]

so the best way is to:

write formula,

plugin values

calculate the values using whatever correct method is on your caclculator

write your answer.

 

[Amna]

yeah i guess :/

 

[Djoyakim]

can u explain how to do this on calculator... in steps..plz

 

[Amna]

okay, these are the steps i would use for finding the sd of, say, 1, 3, 6, 9,
1. find the mean (enter 1+3+6+9, then divide answer by n=4, giving u 4.75)
2. square the answer, save it in the calculator's memory. (=22.5625)
3. find sum of the squares of each term (enter 1^2 + 3^2 + 6^2 + 9^2 = 127)
4. divide answer by the number of terms (127/4 = 31.75)
5. subtract the square of the mean you previously saved from the answer (31.75 - 22.5625 = 9.1875)
6. square root the answer (= 3.03 to 3 s.f.)
that's the standard deviation ^^

 

[Mortal9090]

okay, these are the steps i would use for finding the sd of, say, 1, 3, 6, 9,
1. find the mean (enter 1+3+6+9, then divide answer by n=4, giving u 4.75)
2. square the answer, save it in the calculator's memory. (=22.5625)
3. find sum of the squares of each term (enter 1^2 + 3^2 + 6^2 + 9^2 = 127)
4. divide answer by the number of terms (127/4 = 31.75)
5. subtract the square of the mean you previously saved from the answer (31.75 - 22.5625 = 9.1875)
6. square root the answer (= 3.03 to 3 s.f.)
that's the standard deviation ^^

OH MY!!!

I'll simply use the stat feature!!!!!!

 

[Amna]

lol actually it takes like 20 seconds max, but yeah... when you have a calculator... =P see, few people even do 2+2 in their heads if there's a calculator in sight =P
but it's easier to show some working if u're actually doing the working...