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Q.

The probability of getting a bad pen in a lot of 400 pens is 0.25. Find the number of good pens in the lot.


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a

100

b

200

c

400

d

300 

answer is D.

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Detailed Solution

Given, probability of bad pens = 0.25.  Total number of pens = 400.
The P(A) of the random experiment is,
P(A)=Number of favorable outcomesTotal number of outcomes
Suppose, the number of bad pens is y.
So, the number of the bad pens is,
P(E)=n(X)n(S)
⇒0.25=y400
⇒y=100
Thus, the total number of the good pens are, 400 - 100 = 300
Therefore, the number of the good pens in the lot are 300.
Hence, option 4 is the correct answer.
 
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