# Ex.15.1 Q16 Probability Solution - NCERT Maths Class 10

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## Question

$$12$$ defective pens are accidentally mixed with $$132$$ good ones. It is not possible to just look at a pen and tell whether or not it is defective. One pen is taken out at random from this lot. Determine the probability that the pen taken out is a good one.

## Text Solution

What is known?

$$12$$ defective pens are accidentally mixed with $$132$$ good ones.

Total number of outcomes = $$144$$

What is unknown?

The probability of getting a good pen when $$1$$ pen is picked randomly from the lot.

Reasoning:

This question can be solved easily by using the formula

Probability of an event \begin{align}=\frac{\text{ Number of possible outcomes }}{\text{Total no of favourable outcomes}}\end{align}

Steps:

No of defective pens $$= 12$$

No of good pens $$= 132$$

Total no of pens

$$=12+132\\ =144$$

Probability that the pen taken out is a good one
\begin{align}&= \frac{\text{Number of possible outcomes}}{\text{Total no of favourable outcomes}} \\ &=\frac{132}{144} \\ &=\frac{11}{12} \\\end{align}

Thus, the probability that the pen taken out is a good \begin{align} \frac{11}{12}\end{align}

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