Monday

Rocket bursts into the kitchen holding the porch thermometer. "It read -3 at breakfast. Since then it rose 5 degrees."

"So now it reads 8," he says, already writing the 8 in the Numbers Desk notebook.

Raven taps the paper number line taped to the table. "What do you notice about where -3 sits?"

Rocket looks. "It is left of zero. If I hop 5 to the right, I cross zero on the way."

Nova glides over the table, her light tracing each hop. "Count the hops, not the numbers," she says.

Rocket counts out loud. "-2, -1, 0, 1, 2. It reads 2 now, not 8."

"Field Day scores above and below par work the same way," Raven says. "This week, we hop."

Last week you placed signed numbers on a number line. This week the numbers move.

To add, start at the first number. Then hop the size of the second number.

A positive number hops to the right. A negative number hops to the left.

So -3 + 5 starts at -3 and hops 5 to the right. The hops land on -2, -1, 0, 1 and 2.

The sum is 2. Rocket's 8 came from ignoring the sign on the -3.

Now try 4 + (-6). Start at 4. The second number is negative, so hop 6 to the left.

The hops land on 3, 2, 1, 0, -1 and -2. The sum is -2.

When both numbers are negative, every hop goes left. -2 + (-5) starts at -2 and ends at -7.

A number and its opposite sit the same distance from 0 on opposite sides. 4 and -4 are opposites.

Start at 4 and hop 4 to the left. You land on 0. So 4 + (-4) = 0.

Two numbers that add to 0 are called a zero pair, or additive inverses.

Zero pairs show up everywhere. A score of 3 above par and 3 below par makes par exactly.

A thermometer that rises 6 degrees and then falls 6 degrees is back where it started.

Strong start. You hopped your way to signed sums. Tomorrow you learn why subtracting is just adding the opposite.