Question #1: This will be a Fibonacci Sequence: 1, 1, 2, 3, 5, 8, 13, 21, 34, ...
To get the 7th term to be 6, multiply each term by 6/13, giving:
6/13, 6/13, 12/13, 18/13, 30/13, 78/13, 126/13, 204/13 = 480/13
Question #2: 1,2,-3, 4,5,-6, 7,8,-9, 10,11-12, ...
Adding each set of 3 numbers give this sum: 0, 3, 6, 9, ...
This becomes an arithmetic sequence; to get the sum of the (original) 24 numbers:
Sum = 8(0 + 21)/2 = 84
Then, you must add the 25th number: 84 + 25 = 109
Question #3: The sequence 1, 5, 12, 22, 35, ... Is the pentagonal numbers.
A formula to find the nth number is: Pn = n(3n - 1)/2
So the 10th number is: 10(3·10 - 1)/2 = 145