Question. Liza bought 10 kilograms of butter to make cookies. She used one-half of it for chocolate chip cookies, one-fifth of it for peanut butter cookies, and one-third of the remaining butter for sugar cookies. How many kilograms of butter are left after making those three kinds of cookies?
Answer. 2
What step-by-step reasoning justifies that answer?
Reasoning: Liza used 10 / 2 = 5 kilograms of butter for the chocolate chip cookies. Then, she used 10 / 5 = 2 kilograms of butter for the peanut butter cookies. She used 5 + 2 = 7 kilograms of butter for the chocolate and peanut butter cookies. So, only 10 - 7 = 3 kilograms of butter was left. Then, Liza used 3 / 3 = 1 kilograms of butter for the sugar cookies. Therefore, only 3 - 1 = 2 kilograms of butter were left.