A code has 4 digits, how many codes

Step by step

The question

Question: A code has 4 digits (0 to 9).

How many codes are there?

1 Count the choices

2 Multiply

Every choice goes with every other choice.

So we multiply them all: 10 × 10 × 10 × 10.

This is the counting principle: multiply the number of choices.

Careful!

We do not add the choices.

Every choice goes with every other one, so we multiply.

10 times 10 is 100.

100 times 10 is 1000.

1000 times 10 is 10000.

So there are 10000 codes.

3 Check

Let's check in another order.

First 10 times 10 times 10 is 1000.

Then 10 times 1000 is 10000.

The same.

So the answer is right!

Let's look back.

First: count the choices.

Then: multiply.

Last: check.