Find the missing number: 10, 20, □, 40

Step by step

The question

Question: what is the missing number?

10, 20, □, 40.

1 Find the jumps

2 Find the rule

Every jump is the same: +10.

The rule is: add 10 each time.

3 Use the rule

The number before the box is 20.

20 + 10 = 30.

So the missing number is 30.

4 Check

One more jump from 30 must give 40.

30 + 10 is 40.

Yes!

It works.

Let's look back.

First: find the jumps.

Then: find the rule.

Then: use the rule.

Last: check.