409,200,000,000
rule 1: place point where there is one non-zero number to the left of the decimal point
so that would be after 4
now simply count the number of spaces the decimal point have "moved" from the original number
this will be the exponent of 10
so
409,200,000,000
the point in the original equation was supposed to be at the very end of the number
like this
409,200,000,000.000
we put the decimal point after 4
and now we count
that will be 11 spaces
so our answer is
4.092 * 10^11
