Question

The number 40 has how many significant figures?

Answer 1

Hint: In any value, we need to calculate significant figures which define the level of accuracy. There are some rules to calculate the number of significant numbers.

Complete step by step answer:
First of all, we need the concept behind the significant figures. Significant figures are the digits or numbers that are written in the value in a specific positional notation to specify the accuracy of the measurement or the digits that have some meaning while considering the measurement.
There are few rules to calculate the significant figures in any given value:
In any given value all the non-zero integers are significant.
If there are zero or more than one zero between two non-zero digits, those are also significant.
The zeroes in the starting of any value are not significant.
If there are zeros after a decimal, then those zeroes would be counted as significant
When there are zeros after any whole number and after that zero, we have a decimal specified, then that zero will be counted as significant.
Similarly when there are zeros after any whole number and after that zero, we do not have a decimal specified, then that zero will not be counted as significant.
Exact numbers have an INFINITE number of significant figures. This rule applies to numbers that are definitions. For example, \[1{{ }}meter{{ }} = {{ }}1.00{{ }}meters{{ }} = {{ }}1.0000{{ }}meters{{ }} = 1.0000000000000000000{{ }}meters\]
etc.
For a number in scientific notation: \[N{{ }} \times {{ }}{10^x}\], all digits comprising N are significant by all the rules mentioned above; "10" and "x" are NOT significant.
Thus, by considering all these above-mentioned rules, we can calculate the significant figures for the number $40$.
$4$ is an integer so it is significant but the zero here is not significant because it does not have any decimal after it.
So, the number of significant figures in $40$ is one.

Note: If we had a decimal after zero the number of significant figures would be two, according to the rules mentioned above.