帮忙解答下列数学英语题，会多少解多少，今日毕，急。

S,EandR are all trying to remember the 4 digit combinations for their school lockers

a/S remembers that his combination contains a 4,5,7and 9, but cannot remember the order. how many possible cominations will he need to try?

b/E remember that her combination contains two 5s,a7,and an8. how many possible combinations will she need to try?

c/r remembers that his combination contains three 2s and a 6 . how many possible combinations will he need to try?

2 how many two digit numbers contain a 1 or a 2?

5 in how many ways can four friends A,B,C,Dsit in a row if A and C insist on next to each other?

3 an ice-cream van offers tour flavours of ice-cream:c,v s andl,DONNA is allowed to pick two different flavours for her ice-cream.how many possible flavour combinations could she choose?
不要用函数哦，要用猜测修正法来做，虽然老师有讲不过希望大家再说一遍【因为上课用英语没听太懂呢】how many two digit numbers contain a 1 or a 2? 不用 做 了，我会了

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