Read thermometers and lifts below zero, hop over zero on the number line, and use chips to add and take away. Play, solve missions, crack puzzles and beat the clock.
Start here. A thermometer shows how warm it is. Zero is the freezing point. When it gets colder than zero, the number goes below zero and we call it a negative number. Minus three degrees (−3°) is 3 degrees below zero. A lift in a building can go below the ground floor too: floor −2 is two floors under the ground.
Which is smaller? On a number line, numbers to the left are smaller. So −5 is smaller than −2, even though 5 is bigger than 2. A temperature of −5° is colder than −2°. Every negative number is smaller than zero, and zero is smaller than every positive number.
Hopping over zero. To add, hop right. To take away, hop left. Start at 3 and take away 5: you hop 3 steps to reach zero, then 2 more steps into the negatives, so 3 − 5 = −2. If you owe someone $2, you can say you have −$2.
Chips and zero pairs. Imagine yellow chips for +1 and red chips for −1. One yellow chip and one red chip together make zero, a zero pair. To work out −3 + 5, put down 3 red chips and 5 yellow chips, then remove 3 zero pairs. Two yellow chips are left, so the answer is 2. To take away chips you do not have, add zero pairs first. That is why 2 − (−3) = 5: add 3 zero pairs, take away the 3 red chips, and 5 yellow chips are left.
Distance and absolute value. The distance from a number to zero is its absolute value. Both 7 and −7 are 7 steps from zero. The distance between two numbers is the bigger one minus the smaller one.
Try this above. In Play, set the thermometer to −3, then compare it with −1. Which is colder? On the middle level, start at 3 and take away 5 and watch the frog cross zero. On the hardest level, try 2 − (−3) and look at the chips.
A negative number is a number less than zero, written with a minus sign in front, like −4. You see them in temperatures below freezing, floors below ground, and money you owe.
On the number line −5 is further to the left than −2. It is further below zero, so it is colder, deeper and a bigger debt.
One positive chip (+1) together with one negative chip (−1) is a zero pair. It adds up to zero, so you can add or remove zero pairs without changing the value.
"Just starting" reads and compares temperatures and lift floors. "I know the basics" adds and takes away across zero on the number line. "Challenge me" uses chips for adding and subtracting negatives, absolute value and distance.
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