Question

The standard form of the number $12345$ is

(a) $1234.5\times {10}^1$
(b) $123.45\times {10}^2$
(a) $12.345\times {10}^3$
​​​​​​​(a) $1.2345\times {10}^4$

Answer 1

A number in standard form is written as $a\times {10}^k,$ where $a$ is a terminating decimal such that $1\le a\le 10$ and $k$ is any integer.
So, $12345\times \frac{{10}^4}{{10}^4}=\frac{12345}{{10}^4}\times {10}^4$
$\therefore 12345=1.2345\times {10}^4$