Cake
• This is an intriguing puzzle that came to me on a Sunday afternoon.

What’s the pattern?

5 4 3 2 1
5 3 1
9

7 6 5 4 3
7 5 3
6

9 8 7 6 5
9 7 5
3

11 10 9 8 7
11 9 7
?

Hint #1: Not every pattern is addition. One of the most challenging puzzles (for me) to solve was one by @drewfoster where each number had to be interpreted as a word to solve the puzzle, i.e. 7 needed to be interpreted as the word seven in the puzzle

If 7+5=9+7

What does 20-5 equal?

Hint #2: Sometimes, the pattern is a series of unrelated steps: descending order for 5 integers, descending order of their largest odd numbers.

Hint #3: Engage in math talk with a partner. If you got 9, understand the logic of the person who got 0. Maybe you’re both right. Maybe you’re both wrong.

• What I love about math puzzles, is that someone can come out of left field with a completely different approach that makes you say, “Why didn’t I think of that!”

• My gut reaction is 0.

• Here’s a submission from Chris Marcum, Mathematical Sociologist, via Twitter.