Subtracting 9
🎈 9 is almost 10! Because 9 is just one step away from 10, it has the absolute coolest math shortcut of them all.
Do this: Read the concept below, then try the quiz or activity.
Concept
Get ready for the fastest subtraction trick in the world!
🎯 The "Magic Plus 1" Trick: Because 9 is only 1 step away from 10, subtracting 9 from a teen number is magical.
Example: 15 - 9 = ? All you have to do is take the two digits in the number 15 and add them together! What is 1 + 5? It's 6. So, 15 - 9 = 6!
Let's try another: 13 - 9 = ? Add the digits: 1 + 3 = 4. So, 13 - 9 = 4!
Why does this work? Because instead of subtracting 10, you are subtracting 9. So you subtract a whole bundle, but you have to "give 1 back."
Try it
Let's try the Magic Plus 1 trick!
Instructions: Add the digits of the teen number together to find the answer.
Problem 1: 14 - 9 = ? * Add the digits: 1 + 4 = 5. * Answer: 14 - 9 = ___
Problem 2: 17 - 9 = ? * Add the digits: 1 + 7 = 8. * Answer: ___
Problem 3: 12 - 9 = ? * Add the digits: ___ + ___ = ___ * Answer: ___
Problem 4: 18 - 9 = ? * Answer: ___