The mean of a set of twelve numbers is 5.5. The mean of another set of eight numbers is k. The mean of the combined set of 20 numbers is 8.5. Find the value of k

Answer 1

total of 1st set is 12*5.5
total of 2nd set is 8k
total of two sets is 20*8.5

so, you have

12*5.5 + 8k = 20*8.5
k = 13