For Q 1 & 2 it depends on whether the order of reading is important or not. IE is reading A then B different from reading B then A. From the wording it sounds like order is not important and therefore you are interested in the combination. In that case
I guess the lesson is a small change in the initial parameters can lead to a big difference in the number of combinations.
These two questions sum to one. So the chance of make at least one team = 1 - the chance of making none.
Chance of making none is
Therfore the chance of making at least one is
Another way of seeing this is to draw a Venn diagram.
This is just a straightforward division of number by population so
This is similar to Q4.
In part two you are after an A, B and C in a specific order, so in contrast to Q1 this is a permutation and not a combination.