Everyone knows that magic tricks are fun, but few are aware that math can be too. Whether you are a teacher of this subject or want to have fun with friends, the tricks described in this article will allow you to surprise your "audience".
Steps
Method 1 of 2: Guess Age and Shoe Size
Step 1. Ask a volunteer to write down their age
Hand him a sheet of paper and ask him not to show you the number.
This trick doesn't work with centenarians, but it shouldn't be a frequent problem
Step 2. Ask the other party to multiply the number by 5
Afterward, he has to follow your instructions and solve some calculations. The first thing to do is to multiply the age by 5.
- For example, if he is 42, he should write: 42 x 5 = 210.
- If you wish, let him use the calculator.
Step 3. Ask him to write "0" at the end of the solution
This step is equivalent to multiplying the product by 10, but by simply adding a zero, you make it more complex to go back to the mathematical sequence that underlies the trick.
Considering the previous example, we get the number 2100.
Step 4. Have him add up the date of the day
In truth, the number that is added is not important - you will remove it later - but the current date is a simple value to consider. Remember to say the number out loud so that the other party knows it.
- For example, if today is March 15th, ask the volunteer to proceed with the sum: 2100 + 15 = 2115.
- Tell him to ignore the month and year number.
Step 5. Double the solution
Ask him to multiply the number by two (the calculator is useful at this stage).
2115 x 2 = 4230.
Step 6. Add the shoe size
Ask the person to add this figure (rounded up if it is a half measure) to the last calculated value.
If he wears 39 shoes, he must write 4230 + 39 = 4269.
Step 7. Subtract twice the current date
It is best to do this calculation in mind and then ask the volunteer to subtract the number you propose.
For example, if today is March 15th, do the multiplication 15 x 2 = 30 in your head and ask the other party to subtract 30 from their result 4269 - 30 = 4239.
Step 8. Reveal the magic
Ask him to read the solution aloud: the first two digits indicate the person's age and the last two the size of their shoes.
Method 2 of 2: 1089 makeup
Step 1. Choose a friend who is good enough in math
The trick involves doing a series of additions and subtractions, but people may get confused with the various steps; it is better to have an interlocutor who is able to follow your instructions carefully and who does not make arithmetic errors.
Step 2. Write the number 1089 on a piece of paper that you keep hidden
Announce that you are about to write a "magic number" and proceed without showing it to the public; fold the paper in half.
Step 3. Ask your friend to write a value with three different digits
Make sure he doesn't show it to you and don't tell you; underlines the fact that the various figures must all be different.
- For example, suppose it is 481.
- A calculator may be useful to proceed.
Step 4. Now ask the other party to write the same number, but backwards
He must write down the number on the next line, taking care to write the digits in the opposite order.
In the case considered the inverse of 481 is 184.
Step 5. Proceed to subtract
At this point, the volunteer must subtract the two values, taking care to remove the smaller number from the greater.
481 - 184 = 297.
Step 6. If the solution has only two digits, it must write "0" at the beginning of the number
Ask him to tell you if the result has two digits or three and, if there are two, to write a zero to the left of the first digit without informing you which number it is.
The example considered so far has three digits (297), so you can skip this step; however, it sometimes happens that the difference is 99, so the volunteer has to write "099"
Step 7. Also rewrite this number backwards
Instruct the person to rewrite the difference in the opposite direction. If she had to add a "0", remind her she shouldn't overlook it.
For example, the opposite of 297 is 792.
Step 8. Add the last value to its opposite
The final step is to add the two numbers the person found.
In the example considered above: 792 + 297 = 1089.
Step 9. Show everyone your prediction
Announce that you are able to communicate which is the last number the volunteer wrote; open the sheet of paper and reveal the 1089 solution that you wrote down earlier.
The answer is always 1089. If your friend got a different value, didn't follow your instructions or made a miscalculation
Advice
- Don't repeat the trick in front of people who belong to the same group; for example, predicting the number 1089 for the second time creates far less amazement!
- The 1089 number trick works with most three-digit numbers, even if two are repeated. You can't practice it with those palindromes (for example 161 or 282); by asking the interlocutor to think of a number with three different digits, you can avoid this problem.
- Don't perform the same trick in front of the same person! If you do, he may understand the math and intentionally ruin your next performance by making you "flop". This can be a really awkward situation, especially if you're in front of a large audience or party.
