Question

1 +1+2+2+3+3+4+4+5+5+6+6+7+7+8+8+9+9

Answer 1

The sum of the numbers you've provided, 1 + 1 + 2 + 2 + 3 + 3 + 4 + 4 + 5 + 5 + 6 + 6 + 7 + 7 + 8 + 8 + 9 + 9, is 90.

Answer 2

90

Explanation:

1 +1+2+2+3+3+4+4+5+5+6+6+7+7+8+8+9+9 =

Use the associative and commutative properties of addition to change the order and the grouping of the numbers:

= 1+9 + 1+9 + 2+8 + 2+8 + 3+7 + 3+7 + 4+6 + 4+6 + 5+5

= 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10

= 90