## What you need to know

Standard form is a shorthand of expressing very large or very small numbers. It is sometimes called “scientific notation” because often it is used across all kinds of sciences.

There are strict rules that determine when a number is in standard form. We say a number is in standard when it is written like

$A\times10^n$

Where $n$ must be a whole number, and $1\leq A<10$, or in other words, $A$ must be greater than or equal to 1 but strictly less than 10. For example,

$4.2\times10^5$

is a number in standard form. But what does it actually mean? Well, it’s just a normal number written in an unusual way, so the question really is: what number is it?

Note: decimal notation is the technical term for numbers written in the usual, familiar way.

Example: Write $4.2\times10^5$ in decimal notation.

Firstly, recall that $10^5=10\times10\times10\times10\times10$. Then, we get

$4.2\times10^5=4.2\times10\times10\times10\times10\times10$

To multiply a number by 10 once, we move the decimal point one space to the right. Here, we’re multiplying by 10 five times, so we must the decimal point 5 spaces to the right (if it helps, think of 4.2 like 4.20000). Doing this, we get

$4.2\times10\times10\times10\times10\times10=420,000$

Therefore, we have concluded that $4.2\times10^{5}=420,000$.

Example: Write $2.8\times10^{-4}$ in decimal notation.

This is different because the power is negative, but it’s actually no harder. Firstly, recall that

$10^{-4}=\dfrac{1}{10^4}$

Now, we know $10^4=10\times10\times10\times10$. Having this on the bottom of the fraction means that rather than multiplying by 10 four times, we must divide by 10 four times. Dividing by 10 means moving the decimal point to the left, so moving it 4 spaces left, we get

$2.8\times\dfrac{1}{10\times10\times10\times10}=0.00028$

Therefore, we have concluded that $2.8\times10^{-4}=0.00028.$

So, if the power is a positive number, it’s a big number, and if the power is negative, it’s a small number. Now we’re going to have a look at how to go from decimal notation to standard form.

Example: Write 56,700,000 in standard form.

It says above that the in standard form, your number should be between 1 and 10. So, what we need to do to write this in standard form is: move the decimal point left until this very big number becomes a number between 1 and 10, and then the number of spaces you had to move the decimal point will become the power of 10.

So, if we move the decimal point from the end of 56,700,000 nine spaces to the left, it becomes 5.67, which is between 1 and 10. Therefore, this number written in standard form is

$5.67\times10^{9}$

Remember, it’s a big number, so the power should be positive.

Example: Write 0.0000099 in standard form.

Just like in the last example, we need to move the decimal point until we get a number that falls between 1 and 10, and then count the number of times we moved it. The difference is, the power will be the negative of that number, since it is a very small value we’re dealing.

So, if we move the decimal point in 0.0000099 six spaces to the right, it becomes 9.9, which is between 1 and 10. Therefore, this number written in standard form is

$9.9\times10^{-6}$

Now we’ve seen what standard form is and how to get to/from it, we’re going to take a look at how to multiply/divide. two numbers together without taking them out of standard form. We’re going to be applying the laws of indices; click here (https://mathsmadeeasy.co.uk/gcse-maths-revision/rules-indices-gcse-maths-revision-worksheets/) for more information on them.

Example: Find the standard form value of $(3\times10^8)\times(7\times10^4)$.

We could change both these numbers out of standard form and then do the multiplication then put the answer back into standard form, but that’s a lot of work with no calculator. Instead, we’re just going to change the order around of the things being multiplied. We get

$(3\times10^8)\times(7\times10^4)=3\times7\times10^8\times10^4$

There’s no reason why we can’t do this. We can multiply $2\times5\times6$ and get the same answer as $5\times6\times2$ – when multiplying numbers, order doesn’t matter. We know that $3\times7=21$, and using the multiplication law of indices, we also know that $10^8\times10^4=10^{12}$. So, we get that

$3\times7\times10^8\times10^4=21\times10^{12}$

Great! Well, almost. This answer is not in standard form (21 is not between 1 and 10), and we need it to be. Fortunately, if we recognise that $21=2.1\times10$, then we get that

$21\times10^{12}=2.1\times10\times10^{12}=2.1\times10^{13}$

2.1 is between 1 and 10, so we have successfully completed the multiplication in standard form.

Example: Find the standard form value of $(8\times10^{-5})\div(2\times10^6)$.

This is the exact same idea as the last example. We’re going to break it up and divide the first numbers, 8 and 2, and the powers of 10 separately. Using the division law of indices this time, we get $10^{-5}\div10^6=10^{-5-6}=10^{-11}$, and so we have

$\dfrac{8\times10^{-5}}{2\times10^6}=\dfrac{8}{2}\times\dfrac{10^{-5}}{10^6}=4\times10^{-11}$

4 is between 1 and 10, so this answer is in standard form, and so we are done.

## Example Questions

Because the power is negative, this is going to be a very small number. As the power of ten is -6, we want to divide the number 1.15 by 10 six times, and so we will move the decimal point to the left six spaces. Doing so, we get

$1.15\times10^{-6}=0.00000115$.

Because this is a big number, the power of 10 is going to be positive. In standard form, the number must be between 1 and 10, so we will move the decimal point to the left until we have a number between 1 and 10, and we will count the number of spaces we moved. That number will be the power of 10.

So, if we move the decimal point in 5,980,000 to the left six spaces it becomes 5.98. Therefore, we get that

$5,980,000=5.98\times10^{6}$

We will split up this multiplication, multiplying the initial numbers together and the powers of 10 together separately. Firstly,

$2.5\times6=15$.

Secondly, using the multiplication law of indices,

$10^4\times10^{-9}=10^{4+(-9)}=10^-5$

So, we get

\begin{aligned}(2.5\times10^{4})\times(6\times10^{-9})&=2.5\times6\times10^4\times10^{-9}\\&=15\times10^{-5}\end{aligned}

We’re almost done, but this isn’t in standard form since 15 isn’t between 1 and 10. However, recognising that $15=1.5\times10$, and again applying the multiplication law of indices, we get

$15\times10^{-5}=1.5\times10\times10^{-5}=1.5\times10^{-4}$

This is in standard form, and so we are done.

## Standard Form Teaching Resources

For teachers and tutors looking for standard form resources and revision materials then the worksheets and revision tests above should be exactly what you are looking for. With a range of worksheets to test all abilities and questions that progressively more difficult, hopefully you will find the Maths Made Easy standard form revision resource a useful addition to your portfolio of resources.