SOLUTION: The average of one set of 4 numbers is 35. The average of another set of numbers is 20. The average of the numbers in the two sets is 30. How many numbers are in the other set? ple

Let the number of numbers in other set, be N

Then total of numbers in other set = 20N

As average of numbers in 1st set of 4 numbers is 35, the total of its 4 numbers is: 4(35), or 140

Since average of the 2 sets is 30, we can say that: 

30(N + 4) = 20N + 140 ------- Cross-multiplying

30N + 120 = 20N + 140

30N - 20N = 140 - 120

10N = 20

N, or number of numbers in other set = , or