Chapter 3.2, Problem 4P

Tomaslav has learned the following facts well:

• All the sums of whole numbers that add to 10 or less-Tomaslav knows these facts “forwards and backwards.” For example, he knows not only that $5+2$ is 7, but also that 7 decomposes into $5+2$ or $2+5.$
• $10+1,$ $10+2,$ $10+3,$ …., $10+10.$
• the doubles
$1+1,$ $2+2,$ $3+3,$ …., $10+10.$

For each sum in this problem, describe at least three different ways that Tomaslav could use reasoning, together with the facts he know well, to determine the sum. In each case, write equations that correspond to the strategies you describe. Take care to use parentheses appropriately and as needed.

1. $8+7$
2. $6+7$
3. $8+9$ ( Try to find four or five different ways to solve this.)