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# GCSE Maths/Statistics Probability NEED HELP!!!!! watch

1. Could anyone help me on these Maths questions, Question 2a, Q4, Q5, Q6 and Q7. I'm really struggling so if anyone can provide working outs i will be very grateful, Thanks!
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2. (Original post by moththecat)
Could anyone help me on these Maths questions, Question 2a, Q4, Q5, Q6 and Q7. I'm really struggling so if anyone can provide working outs i will be very grateful, Thanks!
YOU need to show US some working

What rules do you know for combining probabilities?
3. (Original post by davros)
YOU need to show US some working

What rules do you know for combining probabilities?
When combining probabilities you need to multiply both probabilities given. But i need to check my answers as many i have just guessed the answers.

This is what i have got so far.

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4. (Original post by moththecat)
When combining probabilities you need to multiply both probabilities given. But i need to check my answers as many i have just guessed the answers.

This is what i have got so far.

OK, 2 looks good

For 5a I think you've added the probabilities. What would happen using this logic if you tried to calculate the probability she forgets her keys 11 days running? You'd get 11/10 which is bigger than 1! So, how should you combine the probabilities?
5. (Original post by davros)
OK, 2 looks good

For 5a I think you've added the probabilities. What would happen using this logic if you tried to calculate the probability she forgets her keys 11 days running? You'd get 11/10 which is bigger than 1! So, how should you combine the probabilities?
I'm not sure, could you help me on what to do.
6. (Original post by moththecat)
I'm not sure, could you help me on what to do.
Well, how else do you combine probabilities? (You had the right idea earlier!)

I think you need to assume that losing a key on one day is independent of losing it on another day, as you assumed in the earlier example too.
7. (Original post by davros)
Well, how else do you combine probabilities? (You had the right idea earlier!)

I think you need to assume that losing a key on one day is independent of losing it on another day, as you assumed in the earlier example too.
Well there is only one probability given so my guess would be 0.1*0.1=0.01
8. (Original post by moththecat)
Well there is only one probability given so my guess would be 0.1*0.1=0.01
That's right - or you could leave the answer as 1/100 since the original probabilities are given as fractions rather than decimals.
9. (Original post by davros)
That's right - or you could leave the answer as 1/100 since the original probabilities are given as fractions rather than decimals.
Could you help me with Questions 4, 6, or 7.
10. (Original post by moththecat)
Could you help me with Questions 4, 6, or 7.
Q4 is the same principle - seems to be assuming independence again!
11. Could anyone help me on Q5b and 7, i've done the rest.
12. (Original post by moththecat)
Could anyone help me on Q5b and 7, i've done the rest.
For 5b you will have 5 probabilities to multiply together,

Also, remember that forgetting = NOT remembering and vice versa. So how does the probability of remembering relate to the probability of forgetting?
13. 1-PoF=PoR vice versa and finally any ideas on Q7, thank you so much for your help.
14. (Original post by moththecat)
1-PoF=PoR vice versa and finally any ideas on Q7, thank you so much for your help.
Well for (a)(i) does it matter about the green and yellow counters? Could you answer the question if you only had a red counter?

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