求数学两道

Astridcai90UID: 3132551

1. Two competitors battle each other in each match of a tournament with nine participants. what is the minimum number of matches that must occur for every competitor to battle every other competitor?
a. 27   b. 36  c. 45   d. 64  e. 81
答案选B~~~ 不知道解题方法

2. Of 40 pairs of socks in a drawer, x pairs are solid white, y pairs are solid gray, and more than 19 of the pairs are striped
x-y    _____  the number of striped pairs of socks in the drawer.
小于
总觉得不对阿,我觉得存在一个状态,当y=0的时候,两个就是相等的, 但是当y不等于0的时候,就是后面一个大,所以感觉上去选择D嘛, 怎么答案选择B

3. As two wheels----A and B ---- roll across the ground, they both rotate at a rate of 60 revolutions per second. The radius of wheel A is 3. The radius of wheel B is 1.5
the distance wheel A travels per minute   _____   the distance wheel B travels per minute
答案A.
麻烦给下这个轮子什么的公式吧

Namelessone~UID: 3111489

第一道，每个人都要和剩下的8个人比，就是9*8，但是这样两两全都重复算了一次，要除以2.
=0。。。这都行，不算数吧
就是周长啊，A每转一圈的路程都比B大（周长），加起来换成秒换成分钟更是了。