- #1
Addez123
- 199
- 21
- Homework Statement
- Two materials, x1,..,x10 and y1,..y5 (note the 5!) have the following stats:
x_m = 5313
s_x = 5.2
y_m = 5309
s_y = 3
Assume both x and y are the same material, what is the new mean and standard deviation?
- Relevant Equations
- $$s^2 = \frac {1}{n - 1} * \sum (x_i - x_m)^2$$
$$s^2 = \frac {1}{n - 1} * ( \sum x_i^2 -1/n (\sum x_i)^2)$$
The mean is easy to calculate:
(x_m * 10 + y_m * 5) /15 = 5312
Which is correct.
But when you're suppose to calculate the variance it's impossible.
The values are squared so none of the equations will really help me..
(x_m * 10 + y_m * 5) /15 = 5312
Which is correct.
But when you're suppose to calculate the variance it's impossible.
The values are squared so none of the equations will really help me..