1969 Math Trick Part 2

Buzz Aldrin Salutes the Flag

Buzz Aldrin salutes the flag during the Apollo 11 mission in 1969

1969 Math Trick Solution

The answer is… Drum roll, please… 29!!!

Wait, what? How did I know your answer was going to be 29?

The secret to this math trick is to do a little simple algebra.

We started with 1969 and I told you to pick any number between 50 and 1,000 and add it to 1969.

We can represent this algebraically as

1969 + n

Then I asked you to strike out the thousands digit.

Since any number I said you could use would result in a number in the 2,000+ range, striking out the digit in the thousands place would be equivalent to subtracting 2,000 from your answer.  That’s why we limited your choices to 50 through 1,000, we could have said 31 to 1,030 but that would have tipped our hats to the secret of this math trick.  For this trick to work we need to keep the resulting number in the range of 2,000 to 2,999.

Then subtracting the number from the thousands place from the result would require you to subtract the number 2 from the result:

2,000 – 2 = 1,998

Algebraically that would now look like:

(((1,969 + n) – 2,000 – 2)) – n)

which we can reduce to

(((1,969 + n) – 1,998) – n)

We’re adding n and subtracting n so we can further reduce this algebraically to:

1,998 – 1,969 = 29

Now all you have to do is dramatically reveal a card or piece of paper with the number 29 and you look like a math wizard.  If you want to impress your friends and family even more you can change the year to any one you want, just make sure to follow the rules.  For example, lets say you were born in 2004.  In this case you can use any number from 1 to 995, which you can round down to any number you want.  You can see from our example above it doesn’t matter what number they pick as long as it’s in your range so we’ll use 365 again:

+  365

+       2

–   365

Algebraically that would be

(((2,004 + n) – 2,000 – 2)) – n)

which we can reduce to

(((2,004 + n) – 1,998) – n)

We reduce it again to

2,004 – 1,998 = 6

You could take the 6 of Hearts, Clubs, etc., stick it in your pocket and before the person you’re showing the trick gets the answer you whip out the card and say, “Is this your number?”

But before you do that consider subscribing to our newsletter, following us on Facebook, Twitter, and Instagram, or subscribe to our video channel.  Now go try this trick and let us know what happened!

Leave A Comment

Get free STEM activities
in your inbox

Subscribe to our mailing list and get all kinds of STEM activities and updates on KidsSci programs.

Thank you for subscribing.

Something went wrong.