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 251,000.0 in scientific notation, we will have to move the decimal point five points to left, which literally means dividing by 105.
Hence in scientific notation 251,000.0=2.51×105 (note that as we have moved decimal five points to left i.e. divided by105, we are multiplying by 105 to compensate.
