1.

In a hostel, 60% of the students read Hindi newspaper, 40% read English newspaper and 20% read both Hindi and English newspapers. A student is selected at random.Then find the probability of following events : (i). The student reads neither Hindi nor English newspaper. (ii). If the student reads Hindi newspaper, then find the probability that he reads English newspaper. (iii). Find the probability that student reads Hindi newspaper given that he reads English newspaper. (iv). The student reads only English newspaper. (v). The student reads only Hindi newspaper

Answer»

(i). Let event H and E denotes that students read Hindi newspaper and English newspaper, respectively. 

Since, given that in a hostel, 60% of the students read Hindi newspaper, 40% read English newspaper and 20% read both Hindi and English newspapers . 

Therefore, n(E) = 40%, n(H)= 60% and n(H ∩ E) = 20%. 

Now, we know that n(H ∪ E) = n(H) + n(E) − n(H ∩ E). 

Therefore, n(H ∪ E) = 40 + 60 − 20 = 80%. 

Therefore, 80% students who reads either Hindi or English newspaper in the hostel . 

Therefore, 20% students in the hostel who reads neither Hindi nor English newspaper . 

Therefore, the probability that student reads neither Hindi nor English newspaper is \(\frac{20}{100}= \frac{2}{10} = \frac{1}{5}.\)

(By changing percentage into the probability form. ) 

(ii). Now, the probability that student reads both newspaper is P(H ∩ E) = \(\frac{20}{100}= \frac{2}{10} = \frac{1}{5}\)

(By changing percentage into the probability form.)

And the probability that student read Hindi newspaper is P(H) = \(\frac{60}{100}\) = \(\frac{6}{10}\) = \(\frac{3}{5}\) .

Therefore, the probability that student reads English newspaper given that he reads Hindi newspaper is P(E|H). 

Now, P(E|H) = \(\frac{P(H∩E)} {P(H)}\) = \(\frac{1/5} {2/5}\) = \(\frac{1}{3}\) . (Conditional probability)

Hence, if the student reads Hindi newspaper, then the probability that he reads English newspaper is \(\frac{1}{3}\).

(iii). The probability that student read English newspaper is P(E) = \(\frac{40}{100} = \frac{4}{10} = \frac{2}{5}.\) 

Therefore, The probability that student reads Hindi newspaper given that he reads English newspaper is P(H|E).

Now, P(H|E) = \(\frac{P(H ∩ E)} {P(E)}\)  = \(\frac{1/5} {2/5}\) = \(\frac{1}{2}.\) (Conditional probability) 

Hence, if the student reads English newspaper, then the probability that he reads Hindi newspaper is \(\frac{1}{3}\)

(iv). The students in the hostel who reads only English newspaper is n(Eonly) = n(E) − n(H ∩ E) = 40 − 20 = 20%. 

Therefore, the probability that student reads only English newspaper is P (Eonly) = \(\frac{20}{100} = \frac{2}{10} = \frac{1}{5}.\) 

(By changing percentage into the probability form.) 

(v). The students in the hostel who reads only Hindi newspaper is n(Honly) = n(H) − n(H ∩ E) = 60 − 20 = 40%. 

Therefore, the probability that student reads only English newspaper is P(Honly) = \(\frac{40}{100} = \frac{4}{10}\) = \(\frac{2}{5}\)

(By changing percentage into the probability form. ) 

Hence, the probability that student reads only Hindi newspaper is \(\frac{2}{5}\) .



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