Find the missing number: 5, 10, □, 40

Step by step

The question

Question: what is the missing number?

5, 10, □, 40.

1 Find the jumps

2 Find the rule

Every jump is the same: ×2.

The rule is: double it each time.

3 Use the rule

The number before the box is 10.

Double 10 is 10 + 10 = 20.

So the missing number is 20.

4 Check

One more jump from 20 must give 40.

20 + 20 is 40.

Yes!

It works.

Let's look back.

First: find the jumps.

Then: find the rule.

Then: use the rule.

Last: check.