A jar contains 16 marbles, of which 4 are red, 3 are blue, and the res

When you are determining the probability of one event AND another event, multiply the two probabilities together. Add the probabilities if you are determining the probability of one event OR another another event.

Example. The probabilities of chip and dale scoring 700 on GMAT are 1/10 and 1/15 respectively. What is the probability that:

1. Both Chip AND Dale score a 700: Since this is an AND question, you multiply them together. Therefore,
P{both score 700}= \(\frac{1}{10}*\frac{1}{15}=\frac{1}{150}\)

2. Either Chip OR Dale scores a 700: P{Chip scores 700}+P{Dale scores 700}-P{both score 700}= \(\frac{1}{10}+\frac{1}{15}-\frac{1}{150}= \frac{12}{75}\).

gmatpapa, if we have "and" so it is multiplication, and if "or" it means addition?

Total Marbles = 16

R=4
B=3
Y=9

First is red AND second is blue without replacement

to choose first red marble: can be chosen in 4/16 ways, OR 1/4 ways

Now choose second marble without replacement that has to be blue, which can be chosen in 3/15 {3 blue balls, and ONE red ball is already chosen, and not replaced} ways. 3/15 = 1/5

The complete probability of the event (First is red AND second is blue without replacement)

(1/4)*(1/20)

1/20

B

total ways of selecting marbles=16
Total ways of selecting Red marble=4/16
As marbles are not replaced
so ways of selecting blue marble=3/15
so Total prob=4/16 * 3/15=1/4 * 1/5=1/20

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