I have a sum

(this was all marked last week)

the sum is 32.4 billion and it says change to scientific notation.

The teacher says it is 3.24 x 10 to the power of 13.

Not 14.

She also says, that 17.52 in scientific notation is 1.752x 10

because we want it to move by 1 decimal place, so why doesn't the same rule apply for the first sum? Why can't we go 3.24x 10?

Also, there was a sum I saw on the net.

93,000,000 to scientific notation

It says the answer is

9.3x 10 to the power of 7

So why can't we have 3.24x 10 to the power of 14 for the 1st sum?

Please explain, i'm so confused and we have a test tomorrow.

Oh and also, please don't explain too scientifically because I don't really understand wen it is explained in a very complicated way.

Thanks!