Thanks to math you can do many tricks with numbers. For example, you can deduce someone's age by giving precise instructions and doing simple calculations. This person will have the impression that you are performing a magic trick, but in reality you just need to know some information and the mathematical formula will always give you the right answer. With other instructions, you can calculate the month and date of birth as well, or you can use math to give the impression that you are guessing the age of a stranger.
Steps
Method 1 of 3: Deducing a Person's Age Using a Number
Step 1. Ask a friend to choose a number between 2 and 10
To make the trick more fun, you can ask him how many times a week he'd like to eat ice cream, go out for dinner, or something similar. Once he has thought of the number, let him say it.
Let's assume that he chose the number 6. From now on we will use this example
Step 2. Have him multiply the number by 2
He can do this by hand or you can ask your friend to use a calculator for the rest of the trick. Explain to him that he must press equal (=) after each statement.
Example: 6 x 2 = 12
Step 3. Ask him to add 5 to the result
Example: 12 + 5 = 17
Step 4. Have him multiply the number by 50
Example: 17 x 50 = 850
Step 5. Ask your friend if they have already celebrated their birthday this year
If the answer is yes, tell him to add 1767 to the result. If not, 1766.
- Example 1 (completed years): 850 + 1767 = 2617.
- Example 2 (years to be completed): 850 + 1766 = 2616.
- Note that the numbers apply to the year 2017. If you are reading the article in a later year, use 1768 and 1767 in 2018, 1769 and 1768 in 2019, and so on.
Step 6. Tell him to subtract the year he was born
- Example 1: 2617 - 1981 (year of birth) = 636
- Example 2: 2616 - 1981 (year of birth) = 635
Step 7. Consider the final result
The first digit is the chosen number. The other two numbers make up your friend's age.
- Example 1: The answer is 636. 6 is the number chosen at the beginning, 36 is the age.
- Example 2: The answer is 635. 6 is the number thought up by your friend, 35 his age.
Method 2 of 3: Finding a Person's Age Using a Calculator
Step 1. Ask the person to multiply the first number of their age by 5
For example, let's say he is 35 years old. To do the calculations you can use a calculator or a pen and paper. Tell her to press equal (=) after each instruction.
Example: 5 x 3 = 15
Step 2. Tell her to add 3
Example: 15 + 3 = 18
Step 3. Ask her to double the result
Example: 18 x 2 = 36
Step 4. Have her add the second digit of her age to the result
Example: 36 + 5 = 41
Step 5. Ask her to subtract 6
The result is his current age.
Example: 41 - 6 = 35
Method 3 of 3: Use a Calculator to Deduce Month and Day of Birth
Step 1. Enter the number 7
Multiply it by the month of birth. In this example, let's imagine that the person was born on May 28, 1981.
Example: 7 x 5 (month of birth: May) = 35
Step 2. Subtract 1, then multiply by 13
- Example: 35 - 1 = 34.
- Then: 34 x 13 = 442.
Step 3. Add the day of birth
Example: 442 + 28 = 470
Step 4. Add 3
Now multiply by 11.
- Example: 470 + 3 = 473.
- Then: 473 x 11 = 5.203.
Step 5. Subtract the month of birth
Continue by subtracting the day as well.
- Example: 5,203 - 5 (May) = 5,198.
- Then: 5,198 - 28 = 5,170.
Step 6. Divide by 10, then add 11
- Example: 5.170 ÷ 10 = 517.
- Then: 517 + 11 = 528.
Step 7. Divide by 100
The first digit is the month of birth (May). The numbers after the comma indicate the day (28).
