
Wipe Out
Years 3  7

A calculator challenge for one or two players.
Preparation
 One calculator (there's one on your phone)
 Write the title of this challenge and today's date on a fresh page in your maths journal.
Getting Started

 Write this number in your journal.
 Say the number out loud.
 If you said threefivetwo or three fiftytwo they are shortcut ways of saying the number.
 Don't use shortcut names in this activity. They don't tell us enough about the number.
 Say the full name of the number out loud. It has to start with three hundred...
 Write the full number name under 352.

Calculator Challenge
 Write 352 on your calculator.
 Say the number out loud again using its full name.
In this activity you are going to use the 'take away' button. Which one is the 'take away' button?
 In your journal write two other names for the 'take away' button.
You are going to...
but before you do...
 Write the number you will use in your journal.
 Check your prediction with the calculator.


If you are correct you have subtracted just one number, not one digit,
and the screen will show three hundred and two.
If you aren't sure sure ask a someone else.
The answer is at the bottom of the page,
but don't look until you really,
really need to.
Why do you think this challenge is called Wipe Out?
Try these and write the equation each time you get one correct.
Start 
394 
156 
488 
890 
4,689 
Target 
94 
106 
480 
800 
4,009 
Have fun exploring Wipe Out.
Challenge yourself with 3 pairs of numbers, 3 times a week for 3 weeks.

If you are correct,
draw this in your journal
and write an equation on the
arrow to show how to do it.

Challenging Yourself
You can start your challenge with two (2) digit numbers if you want.
 Write two more three digit numbers in your journal. Bigger one on top and an arrow between; or use a Start/Target table.
 Enter the bigger one into your calculator and say it out loud.
 Just using your mind write down the number you think you will have to take away.
 Check on your calculator and write the correct equation.
What happens if you play Wipe Out using addition instead of subtraction?
A True Wipe Out Story
Sandy Drycus, Leadville, Colorado
During the activity Wipe Out, two girls were playing with the number 756. I asked them if they could turn 756 into 56.
After thinking for a moment, one girl confidently replied:
Oh yes, I just need to take away the 7.
She quickly subtracted 7 from 756.
Hey wait a minute. The number is wrong.
What did you get?, I asked her.
I got 749. But look...
She erased 749 and typed back in the number 756.
She put her finger over the 7 on the calculator window.
Now it says 56. All I need to do is take away the 7, but when I did that I got a different number.
I asked,
Yes, I saw that number on your calculator. Why do you think you got that number when you subtracted 7 from 756?
I think my calculator is broke.
Okay. Let's try it again with another calculator.
She then told her partner, who was equally baffled, to type in 756. Again, the girls subtracted 7 and this calculator also gave them the answer 749.
Both girls looked at me and said,
Why is this happening?
If you were Mrs. Drycus, what would you say now
and what would you ask the girls to do?
Explain in your journal.
When you finish you can read the rest of Mrs. D's story below.
Just Before You Finish
Answer this question in your maths journal.
 What do you know now that you didn't know when you started Wipe Out?
Answers & Discussion

More from Mrs. D.
I replied. Let's type 756 back into your calculators. Now read the number to me.
With that hint, the girls read the number over a few times saying, seven hundred, fiftysix.
Suddenly, one girl got so excited she could hardly hit the keys on the calculator as she typed in minus 700. It was truly an 'aha' moment for them when 56 appeared in the window.
The number isn't 7 it is 700. I get it!!
These notes were originally written for teachers. We have included them to support parents to help their child learn from Wipe Out.

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Maths At Home is a division of Mathematics Centre
