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# [Maths] Is this question wrong or me?

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1. I worked this question out from the GCSE Edexcel predicted 2016 higher paper and I am sure it is impossible to prove she earns a profit of £20. My working out done in paint . As you can see the money earned winners is more than she earns altogether. Am I right?
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2. (Original post by Charlie223)
I worked this question out from the GCSE Edexcel predicted 2016 higher paper and I am sure it is impossible to prove she earns a profit of £20. My working out done in paint . As you can see the money earned winners is more than she earns altogether. Am I right?
Your calculation is wrong for P(player winning). There are 3 ways of winning out 20 there the probability is 3/20 not 9/20
3. Hi your calculation is wrong. You need to do a simple space diagram which gives you 3/20 students that would win so 12/80 are expected to win.

80 students X 70p = £56
12 students X £3 = £36

56-36= £20
4. (Original post by TauBilly)
Your calculation is wrong for P(player winning). There are 3 ways of winning out 20 there the probability is 3/20 not 9/20
Ahhh I see, why does my method come to 9/20 are you not allowed to calculate all at once? If you do them all separately it comes to 3/20
5. (Original post by Charlie223)
Ahhh I see, why does my method come to 9/20 are you not allowed to calculate all at once?
You should use a sample space diagram to work out the probability.

It seems like you tried to work it out tree diagram style.
6. (Original post by LieutenantJ)
You should use a sample space diagram to work out the probability.

It seems like you tried to work it out tree diagram style.
Ok, how would this affect my overall marks for the question? would I still get 3 for method?
7. (Original post by Charlie223)
Ok, how would this affect my overall marks for the question? would I still get 3 for method?
Yeah and it would make you less prone to making mistakes. Whenever you have questions like this where you have to work out probabilities with spinners and cards, it is best to use a sample space diagram.

When the probability of two or more events are given and you're asked to work out another probability using the probabilities you already have, then use the tree diagram way.

For example if you have a question like "The likelihood of Tina being late to school each day is 3/10 and the likelihood that she is not is 7/10. Work out the probability that she is late on both Monday and Tuesday." You would use tree diagram way in this instance.

Hope this helps.
8. (Original post by Charlie223)
Ahhh I see, why does my method come to 9/20 are you not allowed to calculate all at once? If you do them all separately it comes to 3/20
The first part is correct, there is a 3/5 chance of picking one that could give you a correct answer. However, for each of those cards chosen only one from the second pile will give you the correct total of 9 so there is a 1/4 chance. This means that the probability of the player winning is 3/5*1/4=3/20

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