Answers to the follow up activity:
1+2= 3
1+2+3= 6
1+2+3+4=10
1+2+3+4+5=15
1+2+3+4+5+6=21
Each line increases by the additional number
You will also notice the sum of fiirst and last is the same as the sum of second and one before the last and the pattern continues
So if you can find the sum of the first and the last and muliply the result by the number of pairs you should be able to get the sum of
the given numbers.
Ex.
1+2+------------(n-1),(n)
Sum of first and last=n+1
Number of pairs = n/2
Therefore sum of all the numbers = {n/2(n+1)}.