1.

A box contains 6 red marbles numbered 1 through 6 and 4 white marbles numbered from 12 through 15. Find the probability that a marble drawn is (i) white (ii) white and odd numbered (iii) even numbered (iv) red or even numbered.

Answer»

Given: box containing 6 red marbles numbered 1-6, 4 white marbles numbered 12-15.

Formula: P(E) = \(\frac{favorable\ outcomes}{total\ possible\ outcomes}\) 

one marble is drawn from the given box, total possible outcomes are 10C1 therefore n(S)= 10C= 10 

(i) let E be the event of getting white marble

n(E)=  4C= 4

P(E) = \(\frac{n(E)}{n(S)}\)

P(E) = \(\frac{4}{10}\) =  \(\frac{2}{5}\) 

(ii) let E be the event of getting white marble with odd numbered 

E= {13,15} 

n(E)= 2

P(E) = \(\frac{n(E)}{n(S)}\)

P(E) = \(\frac{2}{10}\) =  \(\frac{1}{5}\)  

(iii) let E be the event of getting even numbered marble 

E= {2, 4, 6, 12, 24} 

n(E)= 5

P(E) = \(\frac{n(E)}{n(S)}\)

P(E) = \(\frac{5}{10}\) =  \(\frac{1}{2}\)  

(iv) let E1 be the event of getting red marble

P(E1) = \(\frac{6}{10}\) (from(i))

Let E2 be the event of getting even numbered marble 

P(E2) = \(\frac{5}{10}\)  (from (ii)) 

Therefore (E1ꓵ E2) = red coloured and even numbered 

n (Eꓵ E2) =3 

P(E1ꓵ E2) = \(\frac{3}{10}\) 

By law of addition P(E1∪ E2) = P(E1) + P(E2) - P(Eꓵ E2)

P(E1 U E2) = \(\frac{6}{10}+\frac{5}{10}-\frac{3}{10}=\frac{8}{10}=\frac{4}{5}\)



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