At first glance, this might be one of the least intimidating number puzzles you’ll ever see on The 1% Club.

There are no enormous equations, no obscure mathematical symbols and no pages of calculations to work through.

Just a pyramid of numbers.

At the bottom sit 10, 8, 6 and 20. Above them are 9, 7 and one mysterious question mark, followed by 8 and 10, with 9 sitting neatly at the very top.

All you have to do is work out which number belongs in the missing space.

Simple, right?

Well, give yourself 30 seconds before scrolling any further.

Because the more complicated you make this puzzle, the further away from the answer you’re likely to get.

The Pyramid Immediately Tempts You Into Doing Too Much Maths

The obvious instinct is to start searching for some elaborate relationship between the rows.

Perhaps you need to add two numbers and subtract another.

Maybe the numbers are being multiplied or divided.

Could the 9 at the top somehow control everything underneath it?

And then there’s that 20 sitting in the bottom-right corner.

Compared with the other numbers — 6, 8 and 10 — it sticks out immediately, making it tempting to assume there must be some more complicated operation involved.

But that is exactly the sort of thinking that can make a visual puzzle like this so frustrating.

You don’t need advanced maths.

In fact, almost everything you need to solve the question is already demonstrated on the left-hand side of the pyramid.

Can You Spot What 10, 8 And 9 Have In Common?

Take another look at the first two numbers on the bottom row:

10 and 8.

Directly above them is:

9.

Now move one position across.

The next pair is:

8 and 6.

Directly above those numbers is:

7.

That should be your biggest clue.

If you’ve spotted what’s happening, the red question mark suddenly becomes much less mysterious.

But don’t rush.

The pattern also has to explain every other number in the pyramid, including the 8, the 10 and finally the 9 sitting at the top.

Can your answer do that?

One Missing Number Makes The Whole Pyramid Work

This is where the puzzle becomes particularly satisfying.

There isn’t a different rule for each row.

There isn’t a hidden sequence running diagonally through the pyramid.

And you don’t need to treat the 20 as some strange exception.

The same incredibly straightforward operation works its way from the bottom of the pyramid all the way to the top.

Once you see it, those apparently random numbers suddenly fall perfectly into place.

So, final chance before the answer is revealed:

What number should replace the question mark?

The Answer

The missing number is:

13

And the trick is simply to find the average of each pair of neighbouring numbers.

Start at the bottom:

10 + 8 = 18
18 ÷ 2 = 9

That’s why 9 appears above 10 and 8.

Then:

8 + 6 = 14
14 ÷ 2 = 7

That’s why 7 appears above 8 and 6.

Now apply exactly the same rule to the final pair:

6 + 20 = 26
26 ÷ 2 = 13

So the question mark must be 13.

And we can check the rest of the pyramid to make sure it works.

The average of 9 and 7 is 8.

The average of 7 and 13 is 10.

Finally, the average of 8 and 10 is 9 — giving us the number at the very top.

Everything fits.

What initially looks like a pyramid demanding some complicated mathematical formula therefore comes down to one very familiar calculation repeated again and again.

And that awkward-looking 20?

It isn’t there to break the pattern.

It’s there to make the pattern harder to see.