揽瓜阁数学小分队第69天

小白斩鸡

1.问2(10^n)+y 能不能被3整除？

条件⼀：n>6

条件⼆：2+y 能被3整除

2.(n+9)!/[(n+10)!+(n+9)!] 等于1/4!，问n=？

3.总共50个⼈，没有电脑的占20%，没有⼿机的占18%，什么都没有的有3个 ⼈。问又有⼿机又有电脑的有多少⼈？

4.x,y都是正整数 能否判断x是不是偶数？

条件⼀：2x+y=odd

条件⼆：5x+3y=odd

5.a+b 是35倍数，求a+b

条件⼀：a=5m+1

条件⼆：B=7n+3

6.有⼀个marble ball半径为r, ⼀个圆柱形花瓶底部半径为 4r, 瓶内有⽔⾼度为 H1, 将n个ball投⼊⽔中,瓶内⽔的⾼度上升⾄H2, 问如何⽤ r, n 表⽰H2-H1

7.正⽅体体积是否⼤于25？

条件⼀： 表⾯积等于54

条件⼆：所有边长加起来等于36

8.numbers, 20, 30, x (not necessarily to follow this order). is mean smaller than range?

条件⼀： x is smaller than 10

条件⼆：x is greater than 5

9.In xy plane, a circle has its center at origin,and it passes (2, 3),what is the area of the circle.

10.There is a theater with parking lots. it has 17 rows. The first row has 20 lots, the second row has 21 lots, and then each rows behind the 2nd row has 2 more lots than the previous row. How many lots are there in the parking area?

参考答案：

1.B

2.13

3.34

4.C

5.E

6.H2-H1=nr/12

7.D

8.A

9.13派

10.596

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