Use Magic As The Warm-up

If you read enough books, you know you need to grab a student's attention and keep it through the whole lesson.  There are a variety of ways to do this but what about throwing in some mathematically based math.  Yes, you read that right, mathematically based math and its possible to take the steps in the magic and convert it to mathematical steps.

One of the easier tricks is to have a student choose a number between 1 and 100. Make sure they don't share it out loud, but do have them write it down on a card.  Have the student multiply the number by 2.  Then have them multiply the product by 5.  The last step is to have them drop the zero and they will have the number they started with.

Original number is 52.
52 x 2 = 104
104 x 5 = 520
520/10 = 52
The original number.

Another trick is to have a student choose a number between 1 and 100.  Have them double the number and then add ten to the result.  Take the new number and divide it in half.  Next subtract the original number and the answer is 5.

The original number is 28.
28 x 2 = 56
56 + 10 = 66
66/2 =33
33 - 28 = 5.

Try this one with a student.  Have them write down their age.  Then have them multiply their age by 1/5th of 100 (20).  Then add today's date but only the date, not the month or year.  Take this result and multiply it by 20% of 25 (5).  Then add the person's shoe size rounded to a whole number if they take a half size.  The final step is to subtract 5 times todays date.  This should leave a 3 digit number.  The first two give the age and the final two gives the shoe size.

The original age is 25
25 x 20 = 500
500 + 23 = 523
523 x 5 =2615
2615 + 8 = 2623
2623 - (5 x 23) = 2623 -115 = 2508

So the age is 25 and the shoe size is 8.

A final trick is to have a student count the value of the coins in their pocket.  Make sure they don't tell you.  Have the student double the value and then add the first odd prime number to the total.  Then have them multiply the result by 1/4th of 20 before subtracting the lowest common multiple of 2 and 3.  Finally drop the last digit and the result is the amount they started with.

Original amount is 52 cents.

52 x 2 = 104
104 + 3 = 107
107 x 5 = 535
535 - 6 =  529.
If you drop the 9, you are left with 52, the original amount.

One day, use one of these tricks as a warm-up for the class.  Its possible to do any of these tricks with all the students at once.  I've done these before and I've had students work out the math that went with the trick so they saw it both as the trick and as a math problem.  Let me know what you think, I'd love to hear.  Have a great day.