Discover that you can switch the order of numbers in an addition problem and still get the same answer (e.g., 3+5 is the same as 5+3). This 'turn-around' trick cuts the number of facts you need to learn in half!
It's when you switch the order of the numbers you are adding. The answer, or sum, stays the same. For example, \(2+6\) and \(6+2\) are turn-around facts.
$$ 3 + 5 = 8 $$ What is the turn-around fact?
$$ 5 + 3 = 8 $$
If you know \(7 + 2 = 9\), what other addition fact do you know for free?
You also know that \(2 + 7 = 9\).
Does the order matter when you add numbers?
No, the order does not matter in addition. You get the same sum either way.
Solve: \(4 + 6 = ?\) and \(6 + 4 = ?\)
Both equal \(10\). \(4 + 6 = 10\) and \(6 + 4 = 10\).
This math rule is called the Commutative Property of Addition. Can you use it to solve \(1+8\) if you know \(8+1=9\)?
Yes. Since \(8+1=9\), then \(1+8\) must also equal \(9\).
$$ 9 + 3 = ? $$
$$ 9 + 3 = 12 $$
Using the turn-around rule, what is \(3+9\)?
$$ 3 + 9 = 12 $$
Why are turn-around facts helpful?
They reduce the number of addition facts you have to memorize. If you know one, you automatically know its partner!
