5, 15, 25, 35
Their sum is 1200.
All multiples of 12 are also multiples of 6 and they all can be written as the sum of nine numbers.
44
It is: 80 and 100
33, 36, 39, 42
80 and 100
Just 80
64 and 80
They are 4 and all the multiples of 4 up to and including 80
Average of five numbers is 82 so their sum is 82*5 = 410. Average of four of them is 80, so their sum is 80*4 = 320. So the fifth number is 410 - 320 = 90.
The numbers are: 80 and 4