AntiToast

Francisco was so excited about the big game today, that he ate five pieces of toast at breakfast.

"Ouch!" he said. "I ate too much."

Fortunately, his mom had been to the grocery store, and bought some anti-toast. Anti-toast comes from another dimension - it is the exact opposite of regular toast

. antitoast.gif (607 bytes)

When a piece of anti-toast comes into contact with regular toast, there is a loud fizzle and then! -- both of them are gone. They completely cancel each other out.
Francisco, as you recall, was very full after eating five pieces of toast.

He decided to eat three pieces of anti-toast. antitoast.gif (607 bytes)

How many pieces of toast do you think were left?

The three pieces of anti-toast cancelled out three pieces of regular toast like this:

= nothing

=nothing

That left only two of the original five pieces of regular toast:

Francisco was very pleased.

Meanwhile, Meghan was thinking about the school newspaper and wasn't paying attention when she made her breakfast. She wanted to eat two eggs for breakfast... but instead she ate two anti-eggs!

Now she was hungrier than ever!

How many regular eggs did she have to eat just to get back to where she started from?

When Meghan ate one regular egg, it cancelled with the first anti-egg.

+= nothing

When Meghan ate another regular egg, it cancelled with the second anti-egg.

+= nothing

Finally, she was just as hungry as when she started. She fixed her regular breakfast of two eggs and went to school.

Let's write down what just happened with Franciso and Meghan.

Franciso at 5 pieces of toast and 3 pieces of anti-toast. The result was 2 pieces of regular toast.

+ antitoast.gif (607 bytes)

Since 3 pieces of anti-toast are the opposite of regular toast, we could write 3 pieces of Anti-Toast as "-3", since a negative 3 is the opposite of a 3.

This toast and anti-toast equation becomes: 5 + (-3) = 2

Meghan ate two anti-eggs and four regular eggs to have the same result as having eaten two regular eggs.

We can write this as: (-2) + 4 = 2

What do you notice about the equations we've just written...

5 + (-3) = 2, and (-2) + 4 = 2

PE03849_.WMF (8320 bytes)

What does it mean to add negatives?

What do you think would happen if you ate three piece of toast and then four pieces of anti-toast?

+
= ?

Write an equation that describes what happens.

10 + (-7) =

10 + (-15) =

(-6) + 8 =

(-22) + 19 =

100 + (-100) =