#Unsolvable task from my exam

48 messages · Page 1 of 1 (latest)

viscid wren
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(10th grade) we wrote an exam today and there was one task that seemed impossible, but my teacher denied it. afterwards I questioned the others in my class but either they had a obviously wrong answer they thought was right, or they also thought its impossible.

The task at hand went (as far as I can remember) as followed:

Lately there have been more cases of battery damages and display damages in a smarthphone factory. 85% of phones have no damages, while 10% have display damages. create and fully fill in the contingency table.

in the one I used, A = display damage; B = battery damage. the lines above the letters mean No case of the letter below. G stands for Gesamt (German for "Total")

the values I circled are the ones given by the information in the task description, and the rest I simply figured out using the formulas, but I couldnt get any further

IMG_20241023_134144.jpg
surreal ermineBOT
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storm topaz
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That is, assuming you rendered the question correctly.

viscid wren
upbeat ermine
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If you assume they are independent random variables, then you can solve it

storm topaz
upbeat ermine
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Maybe because it's 10th grade, and other wise it's unsolvable

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It's not a good reason, but it might have been part of the problem description that wasn't copied correctly

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If and only if they are independent, then You can use the same ratio: 5 to 85, to fill in the appropriate percentage of the 10% total.

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There is a non-zero chance your teacher doesn't know they had to specify it's Independent and Identically Distributed

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(in real life, of course they are dependent: when you drop your phone, you probably break multiple things at the same time)

viscid wren
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idk

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in the exam I just asked the dude behind me to name a random number from 1-10 that i would then use on (A and B) lol

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at least thered be a chance its right

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and btw yeah it did say the damages arent related forgot to say that

upbeat ermine
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There you go then

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Since the damage isn't related, then the distribution of battery damage is the same regardless of whether the screen is busted. It should be the same proportion

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So the answer is 10/18ths and 170/18ths

storm topaz
upbeat ermine
storm topaz
upbeat ermine
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That many percent

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Probability of B is 1/18

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10% of phones have A. So 10/18 percent. Have A and B

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(percent)

viscid wren
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anyways

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if this is true

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then technically i can sue my teacher

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because we never learnt this

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unless he decides afterwards to just remove that task from the grading

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btw yes he would deserve it, hes that one teacher that says dont be afraid to ask questions but when you do he says oh you learnt this in 6th grade and when you ask again he just ignores

upbeat ermine
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Then 1/18 * 10%

reef summit
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i agree that it’s impossible and would like to add that assuming independence is a very strange thing to do for this question

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it is also possible that your teacher assumed (A and B) to be 0, which is still rather silly

upbeat ermine
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It might be silly for them to be fully unrelated, but regardless, that's the question

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You can't assume A and B are 0, the question said that there are a lot of returns.

reef summit
storm topaz
reef summit
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ah

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i must have missed it

lone eagleBOT
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@viscid wren

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paper bison
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+close