Maths probability question help
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Hello, I need some help with a certain probabiltiy question that is really annoying me.
There are 30 pens in total, 20 of them are black and 10 of them are blue.
Of the 20 Black pens, 8 dont work, while the other 12 work.
Of the 10 Blue pens, 6 dont work, while the other 4 work.
What is the probabilty of picking two pens (no replacement) that are of the same colour and are also working at the same time?
I cant figure out how to do the 'and also working' part correctly!!!!!!!#*#)($# -
Hard at work early in the morning? Take a break
Black - 20/30
Working - 12/20
Blue - 10/30
Working - 4/10
I'm assuming picking 2 pens ONE AFTER ANOTHER, if it's AT THE SAME TIME then make the necessary changes on your own (which I guess, is doable)
1st Black and working - 20/30 x 12/20 = 2/5
2nd Black and working - 19/29 x 11/19 = 11/29
Black and working = 2/5 x 11/29 = 22/145
Blue and working = 10/30 x 4/10 x 9/29 x 3/9 = 2/145
Probability = 22/145 + 2/145 = 24/145
Haven't done probability in a long time. Better get someone to re-confirm first.
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Originally posted by Garrick_3658:
Hard at work early in the morning? Take a break
Black - 20/30
Working - 12/20
Blue - 10/30
Working - 4/10
I'm assuming picking 2 pens ONE AFTER ANOTHER, if it's AT THE SAME TIME then make the necessary changes on your own (which I guess, is doable)
1st Black and working - 20/30 x 12/20 = 2/5
2nd Black and working - 19/29 x 11/19 = 11/29
Black and working = 2/5 x 11/29 = 22/145
Blue and working = 10/30 x 4/10 x 9/29 x 3/9 = 2/145
Probability = 22/145 + 2/145 = 24/145
Haven't done probability in a long time. Better get someone to re-confirm first.
24/145 is correct.