Troy is thinking of buying a new computer that is worth $80. He has initially saved $50 and plans to sell his old computer for $20. How much more money does he need so he could buy the new computer? Give the rationale and then the answer.
Let's think step by step. Troy has $50 + $20 = $70 from his savings and the sales of his old computer. Therefore, he still needs $80 - $70 = $10 more to buy the new computer.. The answer is: 10.

Michelle had some leftover cans of silly string from her birthday party. She split them among Roger and 3 of his friends. Then Roger decided to give 2 of his cans to his brothers so that he now has 4 for himself. How many cans of silly string did Michelle have to start with? Give the rationale and then the answer.
Let's think step by step. Roger originally had 4 cans of silly string + 2 can he gave to his brothers = 6 cans. Since his friends received the same amount as Roger did originally, 3 friends x 6 cans of silly string = 18 cans. Michelle started with 6 cans that went to Roger + 18 cans that went to his friends = 24 cans of silly string.. The answer is: 24.

A class has 60 students. The number of students who bring their lunch is thrice the number of those who eat in the school cafeteria. The rest of the students don't eat lunch. If 10 students eat in the school cafeteria, how many don't eat lunch? Give the rationale and then the answer.
Let's think step by step. Multiplying the number of students eating at the cafeteria by three means that 3 * 10 = 30 students bring lunch. The total number of students that eat lunch is 10 + 30 = 40 students. Since the class has 60 students, those who don't eat lunch are 60 - 40 = 20 students.. The answer is: 20.