I am thinking of a 3-digit number. When you reverse the digits of this number, you get a bigger number, and if you add that to the original number, the sum is 463. What was the number I was thinking of?

Continue reading “Reverse the Digits and Add”# Simple Math

Puzzles and brain teasers involving basic arithmetic and other simple math concepts – very little math knowledge required!

## Matchstick Math 1

Move exactly 1 match to make this a valid equation.

Bonus: find two different ways to solve this.

In matchstick math puzzles, you are not allowed to make an inequality symbol such as ≠, ≥, >, <, or ≤. That would make it too easy!

Continue reading “Matchstick Math 1”## Calculator Error Riddle

A kid is adding consecutive integers on a calculator, one at a time, starting with 1 + 2 + 3 + … and so on. At one point you notice the sum is now 100, but that shouldn’t be possible if the kid was adding this way. The kid tells you that he made an error and *subtracted *exactly one of the numbers he was supposed to add.

What is the number he subtracted?

Continue reading “Calculator Error Riddle”## Eight Eights

Can you arrange eight eights so that the numbers add up to 1000?

Continue reading “Eight Eights”## Guess the Number

Jake has a 4-digit number in mind and asks Raj to guess the number. Raj can have 7 guesses, and Jake will give him some hints after 6 guesses.

Raj makes these 6 guesses:

- 6 3 5 8
- 9 3 0 6
- 4 8 8 2
- 6 7 2 8
- 1 1 9 1
- 5 6 2 7

These were all wrong, but Jake says every guess had exactly one (and only one) correct digit in the correct position. Additionally, all the digits are different.

What should Raj’s 7th guess be?

View Solution## Confusing Zip Codes

The U.S. uses 5-digit zip codes to help determine where mail goes. Since mail can be oriented in all sorts of directions, they avoid assigning zip codes that could be confused with a different zip code when read upside-down. For example, 61666 could be confused with 99919 when upside-down, so mail could be accidentally routed to the wrong zip code if both were actual zip codes.

How many zip codes could be confused with a different zip code when read upside-down?

In the example above, 61666 and 99919 would count as two confusing zip codes. Also, zip codes are allowed to start with 0, such as 00501.

Continue reading “Confusing Zip Codes”## Analog Clock Puzzle

How many times do the hour and minute hands meet on an analog clock every day? What are those times?

Continue reading “Analog Clock Puzzle”## Fix the Equation

Make the following line a valid equation using only these mathematical operators: addition, subtraction, multiplication, division, parentheses, exponentiation, square root, and factorial.

2 2 2 2 = 50

Continue reading “Fix the Equation”## Four Digits Squared

Which perfect square of a 4-digit number has the same last four digits as the original number?

Continue reading “Four Digits Squared”## 24 Game Puzzle

How do you use 3, 3, 8, and 8 to make 24?

Each number must be used exactly once, and only addition, subtraction, multiplication, division, and parentheses can be used.

Continue reading “24 Game Puzzle”