A decimal such as 0.54 would be written as $$5.4*10^{-1}$$.
You have to figure out a way to remove the decimal and so you try placing it in different places. By placing the decimal in between the 5 and 4, we have to use the 10^ notation to correctly identify the original decimal place. So, we would have to move the decimal one place to the left to obtain the original decimal, 0.54. Since we moved it to the left once, we would add a -1 to 10^ giving us $$10^{-1}$$.
Depending on how many times you move the decimal and the direction, your notation of 10^ will change.
For this problem, we would NOT use $$54*10^{-2}$$ because it is incorrect. You can think of having at least 2 numbers such as 2.3, 8.6, 9.0, etc. and then *10^(#) or if you have more significant figures then 2.35, 8.67, etc. But, you notice the decimal is always after the first number, so that is an easy way to convert.
So 0.0057 would start as 5.7...
0.000013 would start as 1.3...
13.46 would start as 1.3 or 1.35...[depending on how many significant figures are required]
In any case, it is easy to remember #.##### as a general rule.
