I have lost touch of JC math for a super super super long time. So i may not be correct at all. But maybe my opinion can in some way helps you.

6d) ermmm i formed the equation but it's very messy. *hard to solve p*

You can consider using graphic calculator to help you. Can solve this method by using graph.

7) is the probability for first part is 1/9?

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I assume we are adding up the numbers on each dice and the sum has to be 10 or greater.

4,6

5,5

5,6

6,4

6,5

6,6

So P is 6/36 = 1/6

Q10) I know i need to define another random variable but still can't solve.

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Part 1.

The first sentence refers to

X ~ B(8, 0.2).

Find P( X>=3). (This is probability for ONE sample of 8 which needed for the 2nd part)

2nd part (which you dont understand)

Y ~ B(100, probabiity you get in part 1)

E(Y) = np = 100 x probability you get in part 1

Q12bii) I tried using 3 different random variable...

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I may go a bit more difficult but i hope you can understand. I will go through part b(i) as well.

I let the answer to 12(a) to be a.

Hence,

for 12b(i),

by letting Y to be the sample has more than two people,

Y ~ B(3, 1 - a)

Question is asking: Find P(Y= 3).

12b(ii),

using secondary school method, you can draw a tree diagram to help you solve.

We need to find the probability of having ONLY 1 person with blood A, and we let the answer be a1.

We need to find the probability of having ONLI 2 persons with blood A, and we let the answer be a2.

Probability of having more than 2 person is already 1-a.

Therefore, answer is a1 x a2 x (1-a) x 6.

Where do i get the 6? By tree diagram you can see there is 6 path to take. By PNC, 6 ways of arranging the different sample.

The important of solving probability qns is first to understand the question and know which method to use. No pt trying with all the diff method and see which one hit the answer. Cuz in real exam, there is no answer for you to refer to. So what you really need to do is NOT TO SOLVE the qns, but have to read the questions and JUST identify the correct distribution to use.