1. ## mean

the price of a CD is denoted by $x. for 60 CDs bought in different stores it is found that sigma(x-12) = 53.40. Calculate the mean price of these CDs. The mean price of a further 40 CDs is found to be$11.64. Find the mean price of the 100 CDs.

The first problem was easy, divide 53.40 by 60 and add 12. BUt with the second one i don't know what method to use i know it must be more complicated than adding the two means and dividing by two

2. if x is the first group of cds and y is the second group then

the mean of the total group is
$\frac{\sum X + \sum Y}{n_x + n_y}$

You know that
${\sum X} = 60 * \bar{X}$
${\sum Y} = 40 * \bar{Y}$

You say you calculated xbar already (although i have not seen and dont follow that method). you are given ybar.

3. Originally Posted by furor celtica
the price of a CD is denoted by $x. for 60 CDs bought in different stores it is found that sigma(x-12) = 53.40. Calculate the mean price of these CDs. The mean price of a further 40 CDs is found to be$11.64. Find the mean price of the 100 CDs.

The first problem was easy, divide 53.40 by 60 and add 12. BUt with the second one i don't know what method to use i know it must be more complicated than adding the two means and dividing by two
$\overline{x} = \frac{60 \, \overline{x_1} + 40 \, \overline{X_2}}{60 + 40}$.