Where is the mistake in my probability calculation for a 20cm string cut?

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SUMMARY

The discussion centers on a probability calculation involving a 20cm string cut into two pieces. The user initially calculated the probability of the shorter piece being between 8cm and 10cm as P(8 ≤ X < 10) = 2 * (1/20) = 1/10. However, the correct probability, as pointed out by the teacher, is 2/10. The mistake lies in the misunderstanding that the shorter piece does not necessarily include the mark, which affects the probability calculation.

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songoku
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Homework Statement
Please see below
Relevant Equations
Continuous Uniform Distribution
1663238891159.png


I want to ask about part (c). This is what I did:

the length of the shorter piece should be 8 ≤ X < 10 so P (8 ≤ X < 10) = 2 . (1/20) = 1/10

But my teacher said the correct answer is 2/10. Where is my mistake?

Thanks
 
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The shorter piece of string does not necessarilly have the mark on it.
 
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I understand. Thank you very much hutchphd
 
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