mcdonalds principles
Simple Math Tricks
There are many ‘math tricks’, which ask you to choose a number or two and work through several steps, often ending up with your original number(s) mixed up somehow, or with a value that’s the same every time.
When they arrive by email, they will often be described as ‘amazing’, or ‘impressive’, as if they were magical.
There isn’t any magic, and you don’t have to be Harry
Potter to understand how these tricks work, or to make
up tricks of your own. All you have to do is look at them the right way, and they’re easy. Two ways to get a new perspective on these puzzles are (a) use zero as your starting number, or (b) don’t pick a starting number, just call it N , and write down the results from all the steps. (If you have to put in two numbers, just use two letters that make sense, such as M for the month and D for the day.)
Here are some examples to try these techniques on:
1
Always Get 1
4
Pick a number.
Add 3.
Multiply by 2.
Subtract 4.
Divide by 2.
Subtract the number you started with.
Tell a friend you can figure how much change she has in her pocket if she will tell you the answer to these steps:
When Is Your Birthday?
The last digit is 9, and the rest are her change!
1.
2.
3.
4.
5.
6.
2
Ask someone to follow these steps:
1.
2.
3.
4.
5.
6.
7.
Multiply the number of the month by 5.
Add 7.
Multiply by 4.
Add 13.
Multiply by 5.
Add the day of the month.
Subtract 205.
The last two digits are the day of the month, and the first digit(s) is the month number. (To make this seem more amazing, have them tell you the result before they subtract 205, and you do that part in your head.)
3
Out For Dinner Mathematics
1. Pick the number of times a week that you’d like to eat out. (Try for more than once but less than 10)
2. Multiply this number by 2.
3. Add 5.
4. Multiply it by 50.
5. If you have already had your birthday this year add
1756. If not, add 1755.
6.
There are many ‘math tricks’, which ask you to choose a number or two and work through several steps, often ending up with your original number(s) mixed up somehow, or with a value that’s the same every time.
When they arrive by email, they will often be described as ‘amazing’, or ‘impressive’, as if they were magical.
There isn’t any magic, and you don’t have to be Harry
Potter to understand how these tricks work, or to make
up tricks of your own. All you have to do is look at them the right way, and they’re easy. Two ways to get a new perspective on these puzzles are (a) use zero as your starting number, or (b) don’t pick a starting number, just call it N , and write down the results from all the steps. (If you have to put in two numbers, just use two letters that make sense, such as M for the month and D for the day.)
Here are some examples to try these techniques on:
1
Always Get 1
4
Pick a number.
Add 3.
Multiply by 2.
Subtract 4.
Divide by 2.
Subtract the number you started with.
Tell a friend you can figure how much change she has in her pocket if she will tell you the answer to these steps:
When Is Your Birthday?
The last digit is 9, and the rest are her change!
1.
2.
3.
4.
5.
6.
2
Ask someone to follow these steps:
1.
2.
3.
4.
5.
6.
7.
Multiply the number of the month by 5.
Add 7.
Multiply by 4.
Add 13.
Multiply by 5.
Add the day of the month.
Subtract 205.
The last two digits are the day of the month, and the first digit(s) is the month number. (To make this seem more amazing, have them tell you the result before they subtract 205, and you do that part in your head.)
3
Out For Dinner Mathematics
1. Pick the number of times a week that you’d like to eat out. (Try for more than once but less than 10)
2. Multiply this number by 2.
3. Add 5.
4. Multiply it by 50.
5. If you have already had your birthday this year add
1756. If not, add 1755.
6.