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# S2 Normal Distribution help watch

1. Can anyone please help with the following question, I am struggling to model my answer. Once that bit is done, I can solve the rest.

"A machine cuts a very long plastic tube into short tubes. The length of the short tube is modelled by a normal distribution with mean m and standard deviation 0.25cm. The value of m can be set by adjusting the machine. Find the value of m for which the probability is 0.1 that the length of a short tube, picked at random, is less than 6.50cm."

Thanks!
2. (Original post by ninuzu)
Can anyone please help with the following question, I am struggling to model my answer. Once that bit is done, I can solve the rest.

"A machine cuts a very long plastic tube into short tubes. The length of the short tube is modelled by a normal distribution with mean m and standard deviation 0.25cm. The value of m can be set by adjusting the machine. Find the value of m for which the probability is 0.1 that the length of a short tube, picked at random, is less than 6.50cm."

Thanks!
P(X<6.50)=0.1 therefore we can find P(Z<... , in terms of m, try it. Drawing a graph may help too.
3. (Original post by raiden95)
P(X<6.50)=0.1 therefore we can find P(Z<... , in terms of m, try it. Drawing a graph may help too.
I did that, but it doesn't come up with the correct answer. I then thought that I should look for 0.1 in the normal distribution tables, but they start at 0.5..
4. The textbook answer is 6.82
5. Never mind I've just worked it out.
6. (Original post by ninuzu)
Never mind I've just worked it out.
Which exam board is this? because I have not started S2
7. (Original post by raiden95)
Which exam board is this? because I have not started S2
OCR. I worked it out by finding 0.95 in the normal tables and making that answer a minus sign. Then solving normally.

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