[Question]50% of substitute teachers walk out after 1 hour of teaching. 30% of the remainder quit before lunch. If 60 substitute teachers show up at 7 AM, how many will be left after lunch?
[Answer]First find the number of substitute teachers left after half quit: 60 teachers / 2 = 30 teachers. Then find how many teachers quit after an hour but before lunch: 30 teachers * 30% = 9 teachers. Then subtract that number from the number of teachers left after one hour to find how many are left after lunch: 30 teachers - 9 teachers = 21 teachers. The answer is 21.

[Question]Mara and Riley went to a carnival, Mara rode the bumper car two times, Riley rode the space shuttle four times, and they both rode the Ferris wheel three times. If a ticket for a bumper car cost $2, a ticket for a space shuttle cost $4, and a ticket for a Ferris wheel cost $5, how much money did they spend?
[Answer]Mara spent $2 x 2 = $4 for riding the bumper car two times. Riley spent $4 x 4 = $16 for riding the space shuttle 4 times. They spent $5 x 3 = $15 each riding the Ferris wheel 3 times. So, they spent a total of $15 x 2 = $30 riding the Ferris wheel. Therefore the total amount they spent at the carnival is $4 + $16 + $30 = $50. The answer is 50.

[Question]If Stu has 9 books and Albert has 4 times as many books as Stu, how many books do Stu and Albert have in total?
[Answer]Albert has 4 * 9 books belonging to Stu = 36 books. So the pair have a combined total of 36 books belonging to Albert + 9 books belonging to Stu = 45 books. The answer is 45.

[Question]There are 20 students in the class. Half of them play basketball. Two-fifths play volleyball and one-tenth play both basketball and volleyball. How many students in this class do not play either game?
[Answer]

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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Half of the students are playing basketball, which means 20 / 2 = 10 students play basketball. Two - fifths plays volleyball, which leaves us with 20 * 2 / 5 = 8 students. One - tenth play both games, which means 20 * 1 / 10 = 2 students. There are 10 + 8 = 18 students who play basketball or volleyball. Among these 18 students, 2 of them are playing both games, so that means 18 - 2 = 16 students play only one of the two games. So finally, 20 - 16 = 4 students do not play either game. The answer is 4.