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 1010.
Note that moving decimal pp digits to right is equivalent to multiplying by 10^p10p and moving decimal qq digits to left is equivalent to dividing by 10^q10q.
Hence, we should either divide the number by 10^p10p i.e. multiply by 10^(-p)10−p (if moving decimal to right) or multiply the number by 10^q10q (if moving decimal to left).
In other words, it is written as axx10^na×10n, where 1<=a<101≤a<10 and nn is an integer.
To write 405,000405,000 in scientific notation, we will have to move the decimal point five points to left, which literally means dividing by 10^5105.
Hence in scientific notation 405,000=4.05xx10^5405,000=4.05×105 (note that as we have moved decimal one point to right we are multiplying by 10^5105 to compensate for division by 10^5105 due to shifting of decimal poimt.
