## osanseviero 2 years ago In a school there are 300 matriculated students (some probability problems)

1. osanseviero

210 of those 300 enter the class. 80% of the students that enter the class get good grades, 15% of the students that dont enter the class get good grades

2. osanseviero

If we chose a random matriculated student, which is the probability of him: 1. Being in the class 2. Don't being in the class and getting good grades 3. Getting good grades

3. osanseviero

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4. osanseviero

a. So 210/300=7/10

5. HawkCrimson

id say so too

6. osanseviero

How to do the second?

7. HawkCrimson

first you find how many students that arnt in the class and are getting gud grades so 90 x 15/100 = 27/2 feel sorry for the student that lost a limb :(

8. HawkCrimson

cause apparently in that class there is half of a student :'(

9. osanseviero

wait a sec, please

10. osanseviero

lol

11. HawkCrimson

haha xD well there 90 students not in the class, and only 15% of the 90 pass, so 90 x 15/100

12. osanseviero

90 persons is the 30% of total

13. osanseviero

are you sure?

14. HawkCrimson

and then 27/2 / 300 = 9/200

15. HawkCrimson

umm, i thought i was xD

16. osanseviero

27/2 is the number of persons that got a good grade

17. HawkCrimson

and didnt come to class but now idk

18. HawkCrimson

normally when i got half a person it was a sign that something went wrong but my reasoning makes sense atleast to me lol

19. osanseviero

Can you repeat your reasoning again? (sorry)

20. HawkCrimson

90 students are people that do not come to class, 15% of these students are students that do well in exams. therefore 90 x 15/100 = 27/2

21. osanseviero

Ok, I see now :D

22. osanseviero

And for the third question?

23. osanseviero

We know that 9 people that did not entered got good grades. We need to see the ones that did come in

24. osanseviero

So 80% of 210

25. HawkCrimson

it would be 210 x 80/100 + 27/2

26. osanseviero

168 entered and passed, 9 entered and passed, so 176

27. HawkCrimson

y 9?

28. osanseviero

the 9 did not enter and did pass*

29. osanseviero

Sooo...176...and 44/75 (check please)

30. osanseviero

Probability of entering and getting a good grade

31. HawkCrimson

but it should be 168 + 27/2 because the number of students that didnt come to class and are getting gud grades are 27/2

32. HawkCrimson

so 195/2 students pass and the probability of the teacher choosing one is 195/2 /300

33. osanseviero

Sorry, internet crashed

34. osanseviero

So 181.5/300

35. osanseviero

Weird numbers :/

36. osanseviero

Last one is: Chance of selecting a student that have passed and entered the class

37. osanseviero

7/10 * 8/10 = 56/100 = 38/50= 19/25

38. osanseviero

So,...yes?