Question 1000955
Probability that A is in the top three brands.
It may occur first, second, or third.
(1/10) for the first, or 0.10
(9/10)*(1/9) for the second, which is 0.10. It can't be first, but all the others can be. 
(9/10)(8/9)(1/8) for the third, which is 72/720 or 0.10.  The first is 9/10, the second is 8/9, because there are nine left and 8 non-As to choose from
The probability is 0.3.
The assumption is that all brands have an equal chance of being chosen.