## kittenbalm Group Title a jar contains 4 green marbles, 5 red marbles, and 7 blue marbles. If two balls are selected randomly what is the probability of getting : 1. 1 green and 1 blue 2. 2 red 3. 1 blue and 1 red 4. 2 blue one year ago one year ago

1. kittenbalm Group Title

2. yrelhan4 Group Title

well i just got confused.. give me a minute.

3. kittenbalm Group Title

okay the title of lesson is combinations i got no idea how to do it lol

4. kittenbalm Group Title

@ganeshie8

5. Zarkon Group Title

are you sampling with or without replacement?

6. kittenbalm Group Title

without i think

7. Zarkon Group Title

then this is a hypergeometric distribution

8. kittenbalm Group Title

a what????? lol explain

9. Zarkon Group Title

suppose you have a box with a red and b green balls. you grab k balls the prob you get r red and g green balls (r+g=k) is given by $\frac{ _aC_r _bC_g}{_{(a+b)}C_k}$

10. kittenbalm Group Title

yeah i dont get it

11. Zarkon Group Title

$\frac{_aC_r\cdot_b C_g}{_{a+b}C_k}$

12. Zarkon Group Title

do you know what $_nC_r$ is ?

13. kittenbalm Group Title

not at all

14. Zarkon Group Title

${n\choose r}$?

15. kittenbalm Group Title

nope i dont know any of this stuff

16. Zarkon Group Title

permutations/combinations?

17. yrelhan4 Group Title

i think it would be easier if we dont use combinations, zarkon.. it would be easier if if we do it like this.. for 1 green ball. 4/16.. 1 blue ball after 1 green ball hass been selected.. 7/15. and then multiply them.. whats your view?

18. kittenbalm Group Title

i knwo thats what this unit is called combinations

19. yrelhan4 Group Title

eh right. so it would be like 4/16*7/15 + 7/16*4/15.. right?

20. kittenbalm Group Title

id think s if that was the case

21. kittenbalm Group Title

wait but youd get the same thing right 7/60 + 7/60

22. yrelhan4 Group Title

yup.

23. yrelhan4 Group Title

then for the second part.. 5/16*4/15.. you get why?

24. kittenbalm Group Title

which would equal 14/60 right because you dont change the denominator right or would it be 14/120

25. yrelhan4 Group Title

yeah.

26. kittenbalm Group Title

so it is 14/120

27. yrelhan4 Group Title

am i right with the second part @RolyPoly ?

28. yrelhan4 Group Title

it should be 14/120..

29. Zarkon Group Title

no

30. yrelhan4 Group Title

14/60.. lol

31. Zarkon Group Title

32. kittenbalm Group Title

well idk how to do this thn i am so lost im gonna fail lol

33. Zarkon Group Title

or 14/60 if you like

34. kittenbalm Group Title

how

35. Zarkon Group Title

the solution is written above

36. kittenbalm Group Title

okay so will you help by showing work on two three and four maybe if i see it on three ill be able to do it

37. RolyPoly Group Title

P(blue first, then green) = P(blue) x P(green after drawing a blue) = 7/16 x 4/(16-1) = a P(green first, then blue) = P(green) x P(blue after drawing a green) = 4/16 x 7/(16-1) = b P(1 blue and 1 green) =P(blue first, then green) + P(green first, then blue) = a + b

38. kittenbalm Group Title

now im deffinately confused i just ned a simple explanation

39. RolyPoly Group Title

2 red, similar, despite the order of picking a red doesn't matter this time, since you don't the red ones are identical

40. kittenbalm Group Title

what omg i need a tutor

41. RolyPoly Group Title

Which part are you confused at?

42. kbrece1 Group Title

2 BLUE

43. kittenbalm Group Title

2 red actually all of it really

44. kittenbalm Group Title

u gonna help k?

45. kittenbalm Group Title

no thats not the question @phi help please