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The first volume of grade six (math contest)
15. Xiao Wang got full marks in the final exam, but when the teacher was marking the paper, Xiao Wang suddenly found that when he was doing a math fill-in-the-blank problem, the final result was a number multiplied by 8 and then subtracted from 63. Because of carelessness, he treated multiplication as division and subtraction as addition, but the number was right. The number of this math problem is _ _ _ _ _ _ _ _ _ _.

17. Divide a group of people into three groups: A, B and C. Everyone must be in one group. It is known that the average ages of A, B and C are 37, 23, 465 and 438+0 respectively. The combined average age of group A and group B was 29 years old. The total average age of group B and group C was 33 years old. Then the average age of this group of people is _ _ _ _ _ _.

18. The sixth-grade students of Le Ballon Rouge Primary School in Tianjin participated in the sports meeting, and everyone chose two of the three events: long-distance running, sprint and relay. It is known that there are 28 people who take part in long-distance running, 25 people who take part in sprint and 33 people who take part in relay. Then, there are _ _ _ _ _ who take part in long-distance running and relay events.

20. Xiao Zhang and Xiao Liu design a set of computer software together, and the reward of * * * is 1 120 yuan. Xiao Zhang works 10 days, Xiao Liu works 13 days, and Xiao Zhang's four-day salary is equal to Xiao Liu's six-day salary. How much does everyone get?