math
posted by kim
The probability of not picking a purple marble out of a bag of marbles is 2/5, if 2 purple marbles are taken out of the bag, reducing the number of purple marbles to 4, what will the new probability of picking a purple marble be?

Sam
3/5 chance beofre of picking a purple marble
3/5 = 2+ 4
the rest of marbles = 4
so 4 / 4+4 = 1/2 
Reiny
Even if tossing around a few numbers often yields the "correct answer", the statements must be mathematically correct and logically sound
look at your statement:
3/5 = 2+4 , now that is news to me, I always thought 2+4 is 6 and not 3/5
Do you see what I mean ?
.....................
If prob of NOT picking a purple is 2/5
then prob of picking a purple is 3/5
We know that originally there were 6 purples, it was given.
let the total number of marbles be x
so we know that 6/x = 3/5
3x = 30
x = 10
so at the start, there 10 marbles, of which 6 were purple
after the takeout, there are 8 left of which 4 are purple
so new prob = 4/8 = 1/2
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