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# Maths Edexcel: A - A* Need Probability Help watch

1. http://prntscr.com/b7z199

Also, is it alright if any of you guys can find me similar questions to this?
Much appreciated
2. There are 3 combinations that give you 9:
1+8
5+4
7+2

She charges 80 students 70p so she will make £56.

There are 3/20 chances of someone getting 9. This means there will be 12/80 chance of getting 9.

So for 12 of the 80 students, she will pay them £3. This is £36.

She made £56 minus the £36 from the number of people who got 9s.
56-36= £20

Hope this makes sense
3. Probability of getting a total of 9 is 3/20. 80 students x 70p is £56.00. 12 students are going to get a total of 9, so 12 x £3 is £36 given to the winners. That leaves her with £20.
4. (Original post by jazz_xox_)

There are 3/20 chances of someone getting 9. This means there will be 12/80 chance of getting 9.
How is there a 12/80 chance of getting 9?
5. (Original post by Divinchi)
How is there a 12/80 chance of getting 9?
Equivalent fractions
6. (Original post by Reisei)
Equivalent fractions
Oh, thanks
7. Hi basically;
1) Find the possibility of getting 9 so the students could get 1&8, 4&5 or 7&2
Then the probability of getting a 1 is 0.2 and the probability of getting 8 is 0.25. multiply these to get 0.05. Then you know the probability of getting the other two outcomes is the same so 0.05 +0.05+0.05= 0.15
2) You know its 0.15 probability of winning so 80x 0.15= 12. 12 students out of 80 will win
3) 80x 0.70= £56. this is how much money she will take but
4) 12x3= £36 so she will give out that much
56-36= 20
She gets £20.

Hope this makes sense and good luck on thursday
8. (Original post by Divinchi)
How is there a 12/80 chance of getting 9?
It's originally 3/20 so I multiplied both the numerator and the denominator by 3, to get the denominator as 80 as this was the number of students. This makes the numerator 12 it would be easier to write on paper than type it on here
9. Probability of picking a card from set A that can match up with a card from set B to make a total of 9 = 3/5
Probability of getting a total of 9, after picking an appropriate card from set A = 1/4

Therefore probability of winning £3 = 3/5 * 1/4 = 3/20 (0.15)

80 students are participating ---> number of students expected to win = 80 * 0.15 = 12
12 * £3 = £36
Costs 70p to play the game ---> total income from game admissions = £0.70 * 80 = £56
Profit = total income minus Laura's expected payout ---> £56 - £36 = £20

Therefore Laura can expect to make a profit of £20.

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