A certain jar contains only b black marbles, w white marbles, and r red marbles. If one marble is to be chosen at random from the jar, is the probability that the marble chosen will be red greater than the probability that the marble chosen will be white ?
1) r/(b+w) > w/(b+r)
2)b-w > r
Jars
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rephrase the question:
P(red marble) > P(w marble) ==> r/(r+w+b) > w/(r+w+b) ==> Is r > w?
Let us begin with Stmt 2 as it looks easier:
b-w>r ==> b>w+r. But this says nothing about relative number of red and white marbles. So insuff.
Stmt1: r/(b+w) > w/(b+r) ==> (b+w)/r < (b+r)/w
Now add 1 to both sides: (b+w)/r +1 < (b+r)/w +1 ==>(b+w+r)/r < (b+r+w)/w ==> r/(b+w+r) > w/(b+w+r) ==> r > w. Sufficient
Answer is A.
P(red marble) > P(w marble) ==> r/(r+w+b) > w/(r+w+b) ==> Is r > w?
Let us begin with Stmt 2 as it looks easier:
b-w>r ==> b>w+r. But this says nothing about relative number of red and white marbles. So insuff.
Stmt1: r/(b+w) > w/(b+r) ==> (b+w)/r < (b+r)/w
Now add 1 to both sides: (b+w)/r +1 < (b+r)/w +1 ==>(b+w+r)/r < (b+r+w)/w ==> r/(b+w+r) > w/(b+w+r) ==> r > w. Sufficient
Answer is A.