this is because Andrea converted the Percentage wrong.
to Convert a Percent to a Decimal, she should have divided by 100
so 5 divided by 100 = 0.05 [not 0.5]
Andrea should have multiplied 300 by 0.05 instead to get the right answer
quickly finding 10% of a number means to simply move the decimal to the left one place
so 10% of 300 is 30
since 5% is half of 10%
half of 30 is 15
and so 5% of 300 is 15