Question

A jar contains some red, black and green marbles. If probability of getting a red marble is $\frac{1}{5}$ and probability of getting a black marble is $\frac{1}{4}$ and jar contains total 11 green marbles, then total number of marbles that were there in the jar is

Accepted Answer

B. Let total marbles = $N$. $P(	ext{Green}) = 1 - \left(\frac{1}{5} + \frac{1}{4}ight) = 1 - \frac{9}{20} = \frac{11}{20}$. Since $P(	ext{Green}) = \frac{11}{N} \implies \frac{11}{20} = \frac{11}{N} \implies N = 40$.

Total number of marbles in jar

Explanation

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