60% of 100 equals 60 right? Yet, she took away 3 apples so therefore we have to divide 60 by 3 to get 20. If each of the three apples were 20% you just need to multiply by whatever number needed to bring that amount to 100%. So therefore, you would multiply 20% by 5 in order to get 100% and that would represent how many apples she originally had.
