Lower Elementary
Question: Mary has a lasagna recipe that feeds 6 people. If the recipe uses 2 ½ cups of cheese. How many cups of cheese will Mary need to feed 15 people?
Answer: 6 ¼ cups of cheese
Upper Elementary
Question: Out of 38 students, 21 students take art class and 20 students take music. If 9 students take both art class and music class, how many students don’t take either class?
Answer: 6 students
Middle School
Question: A little league association has 9 baseball teams. Every team has to play every other team twice. If you attend all the games, how many games do you attend?
Answer: 72 games
Note that if each of the 9 teams plays the other 8 teams once, there will be (9 x 8)/2 games played in order to avoid double counting because team A playing team B = team B playing team A. Since each team plays the other twice, the answer is 9 x 8.
Algebra and Up
Question: What is the last digit of 5,3878457?
Answer: 7
Note that the last digit of 5,3878457 will be equal to the last digit of 78457. Because only the last digit in the base affects the last digit in the answer, we only need to look at powers of 7 to determine the answer. The last digit for the powers of 7 cycle in groups of four. We can see this by looking at the first four powers of 7 we have 71= 7, 72= 49, 73= 343, and 74= 2401. The last digit cycles through the numbers 7, 9, 3, and 1. Because 8457 = 4(2114) + 1, after the last digit cycles through groups of four 2114 times we will end up with the last digit being equal to the last digit of 71, which is 7.
