What is 0.00072 written in scientific notation?

Step by step

The question

Question: write 0.00072 in scientific notation.

There are four choices.

First we solve it, the normal way.

Then we pick.

1 What it looks like

Scientific notation is a number from 1 to under 10, times a power of 10.

2 Move the point

Here is the point.

We move it to the right, until there is just one digit before the point, and it is not 0.

We count the jumps: 1, 2, 3, 4.

4 jumps to the right.

Now it says 7.2.

We moved the point 4 places to the right.

0.00072 is less than 1, so the power of 10 is minus 4: 10⁻⁴.

10⁻⁴ is 1/10000.

So 0.00072 is 7.2 × 10⁻⁴.

3 Check

Let's check: divide by 10000 moves the point 4 back to the left.

We get 0.00072 again!

4 Pick the choice

Our answer is 7.2 × 10⁻⁴.

That is choice B.

5 Why not the others

A is 7.2 × 10⁻⁵.

Wrong: counted 5 places: the point moves 4 places, to after the 7.

C is 7.2 × 10⁻³.

Wrong: counted 3 places: the point moves 4 places, to after the 7.

D is 7.2 × 10⁴.

Wrong: a small number has a negative power.

Let's look back.

First: what it looks like.

Then: move the point.

Then: check.

Then: pick the choice.

Last: why not the others.