In scientific notation, we write a number so that it has single digit to the left of decimal sign and is multiplied by an integer power of 10.
Note that moving decimal p digits to right is equivalent to multiplying by 10p and moving decimal q digits to left is equivalent to dividing by 10q.
Hence, we should either divide the number by 10p i.e. multiply by 10−p (if moving decimal to right) or multiply the number by 10q (if moving decimal to left).
In other words, it is written as a×10n, where 1≤a<10 and n is an integer.
To write 0,0045 in scientific notation, we will have to move the decimal point three point to right, which literally means multiplying by 1000=103.
Hence in scientific notation 0.0045=4.5×10−3 (note that as we have moved decimal three point to right we are multiplying by 10−3.
