- #1

whitefeather

- 2

- 0

## Homework Statement

A class of 20 students takes a test. The score, x , for each student was recorded by the teacher. The results of summarised by:

∑(x-10) = 208 and ∑(x-10)² = 2716

i) calculate the standard deviation of the 20 scores.

ii)show that ∑x² = 8876

iii) Two other students took the test later. Their scores were 18 and 16. Find the mean and standard deviation of all 22 scores.

## Homework Equations

unsure

## The Attempt at a Solution

I tried i, ∑(x-10)² / 20 =varience = 2716/20

standard deviation =√(2716/20)= 11.65

I think this is wrong though because 10 isn't the mean.