Question

Marisa says that to represent the expression - 7 - (-9) on a number line, she should start at -7 and move 9 units to the left. Is she correct? explain why or why not

Answer 1

Given the expression:

$-7-(-9)$

we know as a general rule that if a negative sign is outside of a parenthesis (or any symbol that groups numbers), then the sign of what's inside will change, then we have the following:

$-7-(-9)=-7+9$

On the number line, this addition looks like this:

notice that we have to move 9 units to the right, therefore, Marisa is not correct.