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Where would I start with this question:

Consider the attached table which summarises grades (high or low) awarded to $200$ students split by the examiner ($1, 2$ or $3$) who graded the paper. If examiner #$1$ grades your paper, what is the probability that you get a low grade?

enter image description here    

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closed as off-topic by Saad, Davide Giraudo, Strants, The Phenotype, A. Goodier Mar 15 '18 at 17:30

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    $\begingroup$ What do you think? $\endgroup$ – lulu Mar 15 '18 at 11:33
  • $\begingroup$ Welcome to stackexchange. You are much more likely to get help rather than votes to close and downvotes if you edit your question to show what you tried and where you are stuck. $\endgroup$ – Ethan Bolker Mar 15 '18 at 11:35
  • $\begingroup$ I would say that it's the number of low grades divided by the total number of grades. And if you're only looking at a specific examiner, then consider only the values pertaining to them. $\endgroup$ – Matti P. Mar 15 '18 at 11:35
  • $\begingroup$ i am new to probability and when reading this question it hard for me to pull out the info i need to get started, sorry if it seems that its not tried just cant get my head around it. $\endgroup$ – enzof60 Mar 15 '18 at 11:44
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According to the table (in case you can't access to the image):

  • Examiner #$1$ awards high grades for $20$ students, low grades for $25$ students, $45$ in total.

  • Examiner #$2$ awards high grades for $26$ students, low grades for $19$ students, $45$ in total.

  • Examiner #$3$ awards high grades for $36$ students, low grades for $74$ students, $110$ in total.

  • A total of $82$ high grades and $118$ low grades are awarded.

For this problem, I will consider that all students are not studying well enough to guess if they get a high grade or not (if they are learning properly, they will sure that they get a high score!).

Examiner #$1$ grades $45$ tests in total ($100$%), which includes $20$ high-grade tests ($44.4$% of all examiner #$1$ tests) and $25$ low-grade tests ($55.6$%), so if the examiner #$1$ grades your test, there is a $55.6$% chance that you will get a lower score.

Similarly, you can calculate for the other two examiners by using:

$\text{Percentage of low grades(%)}=\frac{\text{Number of low-grade students}}{\text{number of students in total}}\times 100$

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  • $\begingroup$ feel a little silly now that i see now its done, as i thought there was some hidden agenda were you might also need to do something with the other scores on the table. thanks for the help greatly appreciated. $\endgroup$ – enzof60 Mar 15 '18 at 14:00

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