Find the sum of the sequence.
39 +40 +41 +42 + + 138

Sol1 you can use "first(first+last)/2" is 138(138+1)/2 - 38(38+1)/2 = 8850

Sol2 or you can look this 39+40+41++100+(100+1)+(100+2)++(100+38) = 1+2+3++99+100+100(38) = 5050+3800 =8850

-250

Step-by-step explanation:

We could solve the problem above using integers. Integers are the set of whole numbers and their opposites. The number line is used to represent integers. So, when it is a 'decrease' it is negative.