Standard form
Sections:
1) Revision notes
2) Practice questions
Revision notes
What is standard form?
$$ a \times 10^n$$
Standard form is a way of writing large numbers or small numbers using powers of $10$.
- $1 \le a < 10$
- $n$ is an integer
The number $6.7 \times 10^{67}$ is in standard form. On the other hand, the number $0.12 \times 10^{-12}$ is not in standard form since $0.12$ does not satisfy $1 \le a < 10$.
How to express numbers in standard form
Express large numbers in standard form
$ 52900 = \phantom{.} $ $ 5.29 \times 10^4 $
Sometimes, the number is already written using powers of $10$, but it is not yet in standard form. For the following example, since $3845.7$ does not satisfy $1 \le a < 10$.
$ 3845.7 \times 10^4 = \phantom{.} $ $ 3.8457 \times 10^7 $
Express small numbers in standard form
$ 0.0342 = \phantom{.} $ $ 3.42 \times 10^{-3} $
$ 0.008 \phantom{.} 291 \times 10^{-4} = \phantom{.} $ $ 8.291 \times 10^{-7} $
Convert from standard form to ordinary numbers
To convert a number from standard form to an ordinary number, use the power of $10$ to decide where the decimal point moves.
$ 4.37 \times 10^5 = \phantom{.} $ $ 437 \phantom{.} 000 $
$ 6.82 \times 10^{-4} = \phantom{.} $ $ 0.000 \phantom{.} 682 $
For very large or very small numbers, the calculator may display the answer in standard form, such as $3.84 \times 10^{12}$ or 3.84E12.
Prefixes: millions, billions and trillions
$ 1 \text{ million} = \phantom{.} $ $ 1 \times 10^6 $
$ 1 \text{ billion} = \phantom{.} $ $ 1 \times 10^9 $
$ 1 \text{ trillion} = \phantom{.} $ $ 1 \times 10^{12} $
Convert numbers with prefix to standard form
$ 0.455 \text{ million} = \phantom{.} $ $ 4.55 \times 10^5 $
Convert from a number to a number with prefix
$ 7.38 \times 10^8 = \phantom{.} $ $ 0.738 $$ \text{ billion}$
Practice questions
Arithmetic operations involving standard form
1. Simplify $ (2.8 \times 10^6) \div (3.5 \times 10^7) $, leaving your answer in standard form.
Answer: $ 8 \times 10^{-2} $
2. (a) Express $4.8 \times 10^{-5}$ in the form $A \times 10^{-4}$.
Answer: $ 0.48 \times 10^{-4} $
2. (b) Hence, without using a calculator, simplify $ 7.1 \times 10^{-4} - 4.8 \times 10^{-5} $, leaving your answer in standard form.
Answer: $ 6.62 \times 10^{-4} $
Place value with powers of 10 (from O Level 2005)
3. The number $3002.05$ can be written as $3 \times 10^x + 2 \times 10^y + 5 \times 10^z$. Given that $x$, $y$ and $z$ are integers, find the values of $x$, $y$ and $z$.
Answer: $ x = 3, y = 0, z = -2 $
Problems in real-world context involving standard form
4. In $2024$, the population of Country A was $10.1$ million. The population of Country B was $3.4 \times 10^7$.
(a) Express the population of Country A in standard form.
Answer: $ 1.01 \times 10^7 $
(b) Find the difference in population between Country A and Country B, expressed as a percentage of the population of Country A.
Answer: $ 237 \% $
O Level past year questions on standard form
| Year & paper | Comments |
|---|---|
| 2024 P1 Question 18 | Arithmetic operations involving standard form |
| 2023 P1 Question 24 | Problem in real-world context |
| 2023 P1 Question 1a, b | Problem in real-world context |
| 2021 P2 Question 2 | Problem in real-world context |
| 2019 P2 Question 3c | Problem in real-world context |
| 2017 P2 Question 2 | Problem in real-world context |
| 2015 P1 Question 4 | Problem in real-world context |
| 2014 P2 Question 2 | Problem in real-world context |
| 2013 P1 Question 21 | Problem in real-world context |
| 2012 P2 Question 4c | Problem in real-world context |
| 2011 P1 Question 22 | Problem in real-world context |
| 2010 P1 Question 14 | Problem in real-world context |
| 2009 P1 Question 21 | Problem in real-world context |
| 2008 P1 Question 1 | Arithmetic operations involving standard form |
| 2008 P1 Question 7 | Problem in real-world context |
| 2007 P1 Question 22 | Problem in real-world context |
| 2006 P1 Question 10 | Problem in real-world context |
| 2005 P1 Question 4a | Compare magnitude of numbers in standard form |
| 2005 P1 Question 5 | Problem in real-world context |
| 2005 P1 Question 18a | Place value with powers of 10 (see question 3 above) |