Consider the question. Kelly needs school supplies to teach her class for an art project. She has 8 students and they will need 3 pieces of construction paper each. In addition to the construction paper, she needs to buy 6 bottles of glue for everyone to share. After Kelly purchases these supplies, she dropped half of them down a storm drain. Class is about to start, but she manages to rush to the store and buy 5 more pieces of construction paper. How many supplies are left?
 If the answer is '20'; explain the reasoning:
Kelly needs 8 * 3 = 24 pieces of construction paper. She buys glue which grows the supplies to 24 + 6 = 30. Unfortunately, she dropped 30 / 2 = 15 supplies. Rushing to the store, she buys more construction paper bringing her supplies back to 15 + 5 = 20.