Question

Explain how to find the sum 3 + -9using chips, a number line, or the rules for adding integers. Give the answer with your explanation.

Answer 1

There is no extra dollar.

The three men paid $30 for a room.
The manager realized that the room only
ought to have cost them $25, so he sent
the bellhop back with $5 to be returned
to them.

Out of the original $30, here's where
it all went:

Kept by motel: $25
Stolen by bellhop: 2
Returned to men: 3
---
Total: $30
===

Another way of looking at it: The
three men ended up paying a total of
$9×3=$27. That's $25 for the room
plus the $2 stolen by the bellhop.

The question tries to trick you into
adding the $2 stolen by the bellhop to
the total of $27 that the three men end
up paying, for a total of $29, and then
wondering why it doesn't add up to the
original $30. But this is nonsense, as
the $27 already includes the stolen $2
($25 for the room plus the stolen $2
equals $27).

The $27 that the men ultimately end up
paying, plus the $3 that was returned
to them, adds up to the original $30. The
$25 that the men were supposed to pay
for the room, plus the $5 that the bellhop
was supposed to return to them, equals the
original $30.

Read more: 3 people pay $10 each for a motel room for $30. The manager over charges them and gives $5 in ones to the bellhop to return to them, he keeps $2 for himself. Where did the extra dollar go, if each person only paid $9?

Answer 2

just an e.g. @brt12