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# Alevel Maths Help watch

1. A biased coin is thrown twice. The probability that it shows heads both times is 0.04. Find the probability that it shows tails both times.

Another coin is biased so that the probability that it shows heads on any throw is 'p'. The probability that the coin shows heads on exactly one in two throws is 0.42. Find the possible values for 'p'
2. (Original post by Alexia_17)
A biased coin is thrown twice. The probability that it shows heads both times is 0.04. Find the probability that it shows tails both times.

Another coin is biased so that the probability that it shows heads on any throw is 'p'. The probability that the coin shows heads on exactly one in two throws is 0.42. Find the possible values for 'p'
Have you made any progress? Please post all your working. There are only two events here (two coin tosses) so drawing a probability tree may help.
3. (Original post by Alexia_17)
A biased coin is thrown twice. The probability that it shows heads both times is 0.04. Find the probability that it shows tails both times.

Another coin is biased so that the probability that it shows heads on any throw is 'p'. The probability that the coin shows heads on exactly one in two throws is 0.42. Find the possible values for 'p'
Hey there
on first question, take the square root of 0.04. then it should be easier for you

second:
try pq = .42 (q=1-p) Do note that pq is exactly one in 2 throws being a success.
also make a probability tree for it. that *may* help you a bit.
4. (Original post by ThatsAGoodOne349)
Hey there
on first question, take the square root of 0.04. then it should be easier for you

second:
try pq = .42 (q=1-p) Do note that pq is exactly one in 2 throws being a success.
also make a probability tree for it. that *may* help you a bit.
Thank you,
I have managed to get p2-p+0.42=0, however this doesn't work youing the quadratic formula and i can't seem to work out where I have gone wrong.
5. (Original post by Alexia_17)
Thank you,
I have managed to get p2-p+0.42=0, however this doesn't work youing the quadratic formula and i can't seem to work out where I have gone wrong.
do you have a probability tree
6. (Original post by ThatsAGoodOne349)
do you have a probability tree
Thank you, I have realised that you need to half the 0.42 now. I have a couple of other questions which I am struggling on. Would I be able to private message you them to see if you could help?
7. (Original post by Alexia_17)
Thank you, I have realised that you need to half the 0.42 now. I have a couple of other questions which I am struggling on. Would I be able to private message you them to see if you could help?
I did a level maths so I'll help as best I can
8. (Original post by Alexia_17)
Thank you, I have realised that you need to half the 0.42 now. I have a couple of other questions which I am struggling on. Would I be able to private message you them to see if you could help?
It would be preferable if you post them here so that others can benefit in the future from the same question.
9. (Original post by Notnek)
It would be preferable if you post them here so that others can benefit in the future from the same question.
if i post what?
10. (Original post by Alexia_17)
if i post what?
You said you were going to private message some questions. We prefer it if people post questions in the public forum instead of via PM.
11. The probability that a student forget to do their homework is 5% independently of other students. If at least one student forgets to do homework, the whole class have to sit a test.
a) There are 12 students in a class. Find the probability that the class will have to do a test.
b) Using the expression 1-(0.95)n find the smallest number of students in the class such that the probability that the class wil have to do a test is at least 80%

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