Simple Math

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

Difficulty - Easy, Matchstick Puzzles, Simple Math

Matchstick Equation 4

Move exactly 2 matches to make this a valid equation.

Bonus: find more than one solution.

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

Difficulty - Easy, Simple Math

Most Frequent Digit

What is the most frequent digit among the numbers between 1 and 1000 (inclusive)? Consider only base-10 whole numbers.

Difficulty - Very Easy, Simple Math

Zero-less Factors

What two numbers contain no zeroes and can be multiplied together to produce 100000?

Difficulty - Medium, Interview Brain Teasers, Simple Math

How Many Friday the 13th in a Year

Some consider Friday the 13th (any Friday that falls on the 13th day of a month) unlucky.

In a calendar year, how many Friday the 13th can occur? Find both the minimum and maximum.

Difficulty - Hard, Simple Math

Consecutive Numbers Grid Puzzle

13
		10
	4	16
	7

The cells in this 4×4 grid puzzle contain the numbers 1-16 each once. There are two rules to the arrangement of the numbers:

Any two consecutive numbers must share a row/column (1 and 16 should be considered consecutive).
No row/column can contain three consecutive numbers.

Fill in the remaining numbers.

Difficulty - Medium, Matchstick Puzzles, Simple Math

Matchstick Math 3

Rearrange exactly 2 matches to make this a valid equation.

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

Difficulty - Medium, Interview Brain Teasers, Number Theory, Simple Math

I Like the Numbers 4 and 5

I like the numbers 4 and 5. I like to add 4’s and 5’s together to make other numbers, such as 4 + 4 + 5 + 5 + 5 = 23. How many numbers from 1 to 1000 can be written as the sum of 4’s and 5’s?

Difficulty - Easy, Riddles and Lateral Thinking, Simple Math

Password to Exclusive Club

A man wants to enter an exclusive club, but doesn’t know the password. He observes a few other patrons:

First patron walks up and the doorman just says “12”. The patron replies “6” and is let in.
Second patron walks up and the doorman says “6”. The patron replies “3” and is let in.

Thinking he has figured it out, the man walks up and the doorman says “10”. The man replies “5” but it’s incorrect and he is turned away.

What should the man have said instead?