Easy GRE question: Statistics I'm not sure how to set this statistics problem when they give me a group of arbitrary values. Can someone help?
A group of 20 values has a mean of 85 and a median of 80. A different group of 30 values has a mean of 75 and a median of 72.
a) What is the mean of the 50 values?
b) What is the median of the 50 values?
Thank you

The formula to find mean is 
Mean=
(total number of values) ÷ (quantity of values) 
So, as we know the mean and the quantity values of the first group is, 85 and 20. (It is given) 
So we can substitute the values into the formula and get the (total number of values) 
Same goes to the other group that contains 30 values... 
The trick of the question is... They gave you the values, mean and median, of (group of 20 values) and (group of 30 values). And asked the mean and median of the combined group. (Group of 20 values and group of 30 values) 
So workouts are...
85=(sum of x values)÷20
20(85)= (sum of x values)
     X= 1700
75=(sum of x values)÷30
30(75)=(sum of x values)
     X=2250
So... 30+20=50
So... Mean of the group of 50values is..
Mean= (1700+2250)÷50
    = 3950÷50
    = 79 
And.. For question b).. 
The median cannot be identified with the given information in the question. 
