What is the scientific notation for 45?

##4.5 * 10^1##, but also depending on precision.

One of the uses of is to show how many significant digits there are, which is basically a show of precision.

For example, a figure like 4.5000 is technically just 4.5, but it is accurate to the nearest ten-thousandth as denoted by the trailing zeroes.

Since a figure like 250 can be ambiguous if it has 2 sig. figs. or 3, when expressed as ##2.50*10^2## we know it is accurate to the singular unit and not, say the nearest tens value.

So depending on how you got that value of 45, it can be ##4.5*10^1## (And usually this is the case), but sometimes, it may be taken as ##4.5000000 *10^1## because maybe it is a constant and therefore "infinitely precise", but you used that many sig. figs. because you will be operating with numbers of a similar number of sig. figs.

Remember, precision can matter a lot.