Question. Isabel has some money in her piggy bank. She spent half the amount and bought a toy. She then spent half of the remaining money and bought her brother a book. If she has $51 left, how much money, in dollars, did she have at first?
Answer. 204
What step-by-step reasoning justifies that answer?
Reasoning: After buying the toy, Isabel has 51 * 2 = 102 dollars left. Isabel had 102 * 2 = 204 dollars at first.