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

## 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 \(\begin{align} \frac{11}{12}\end{align}\)