The diagram shows 7 cards, each with a digit printed on it. The digits form a 7 -digit number.
1
3
3
3
5
5
9
How many different 7 -digit numbers can be formed using these cards?
The diagram below shows 5 white cards and 10 grey cards, each with a letter printed on it.
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From these cards, 3 white cards and 4 grey cards are selected at random without regard to order.
(a) How many selections of seven cards are possible?
(b) Find the probability that the seven cards include exactly one card showing the letter A .