Math Topic: Number Sense

Subtopic: Place Value

Grades: 3-5

Spider’s at it again with these number tricks that are easy for students to learn and fun to play on family and friends. See if your students can use the power of numbers to become math magicians!

Learning Objective: Students practice mental arithmetic while learning magic tricks.

NCTM Standard: Number & Operations

DIRECTIONS

Class Periods: 1

Mind Reader

To do this trick, students work in pairs. Have them take turns playing magician.

1. The student playing the magician asks another student to hide a penny in one hand and a dime in the other.

2. The magician tells the student holding the coins to do the following:

a. Multiply the value of the coin in the right hand by any odd number. (The student may want to jot down the answer.)

b. Multiply the value of the coin in the left hand by any even number.

c. Add the two numbers together and say the total.

3. The magician determines whether the total the other student says is odd or even and then announces which hand has the penny!

How It Works

If you multiply a penny (1) times an even number (when it’s in the left hand) its product is even. If you multiply it times an odd number (when it’s in the right hand) its product is odd. The product of the dime (10) will always be even. So there are only two possibilities:

Penny in the right hand: Odd + Even = Odd

Penny in the left hand: Even + Even = Even

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Mystery Dice

This trick gives students practice adding and subtracting in their heads as they “see through” dice! Have students work in pairs and take turns playing magician.

1. One student plays magician and announces that he or she can see through a pair of dice and tell the total of the numbers hidden face down after the dice are rolled.

2. The second student rolls the dice.

3. The magician mentally adds the numbers on top, subtracts them from 14 and announces that number—the hidden sum!

How It Works

For each die, opposite sides add up to seven. If you total the top and bottom sides for both dice you always get 14. If you total the top numbers and subtract them from 14, you get the sum of the sides hidden from view.

Cyberchase Episode: “And They Counted Happily Ever After”

Hacker kidnaps the King of this fractured fairy tale world, and demands a ransom of golden eggs. The Wicked Witch then casts a spell, taking away everyone’s ability to count and making it impossible for the fairy tale folk to gather the required large number of eggs. With the safety of the King at stake, the kids must help the fairy tale folk understand the role of place value in our number system before time runs out!

The Big Idea: Let numbers stand for things in a regular pattern, and you have the power to keep track of anything and everything on Earth.

Cyberchase FOR REAL (Epilogue)

Hoping to pick up some pointers to improve the way she runs, Bianca volunteers to count runners in a marathon and uses an abacus to keep track.

Online games featuring similar math themes:
Number Machine
(Players use place value to rearrange random digits to make a 3 digit number larger than Hacker’s)