You have a box containing 6 white, 4 red, and 8 black marbles. You pick a marble and it is red. You then pick a white marble. On
the third attempt, you pick a white marble again. What are the chances that on the fourth try you will pick a black marble? (Hint: You have not replaced the marbles you picked).
2 answers:
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From any proportion, we get another proportion by inverting the extremes (or the means):
so we have:
2x=3k
2x+y=2k therefore:
3k+y=2k
y= - k
x=
The corect answer is A. -3/2
or:
From any proportion, we get another proportion by inverting the extremes and the means:
We use a property of proportions:
so we have
3y = - 2x