For example, in scientifi c notation, we say that the Sun has a mass of 1·988 × 10 30
as it is easier to write than 1 988 000 000 000 000 000 000 000 000 000 kg. A lightyear (the distance light travels in one year) is written as 9·461 × 1015
rather than 9 461 000 000 000 000 metres.
Writing numbers greater than or equal to 10 in index notation
1
2 3
Move the decimal place to the left until the number is equal to or greater than 1 and less than 10
Count the number of times you had to move the decimal place to the left in step 1 Write × 10 n
after the new number, where n is the number of times you moved the decimal place to the left
Worked example 1 Write the following numbers in scientifi c notation (i) 8 000
Solution (i)
(ii)
kg, metres,
Index (or scientifi c) notation is when a number is written in the form a × 10 n
, where a is a number
equal to or greater than 1 and less than 10 ( 1 ≤ a < 10 ) and n ∈ ℕ
(ii) 62 573.78
Converting from index (scientifi c) notation to a regular number
When the power of 10 is a positive number, n, move the decimal place n times to the right to change a number from index form back to a regular number.
Worked example 2 The distance between Mars and the Sun is at least 2·279 × 10 8 Write this distance as a regular number.