Question

There are two bags. One bag contains 4 blue pens and 3 black pens. The other bag contains 7 red pens and 3 black pens. If a bag is selected at random and from it, a pen is drawn, the probability that the pen is black is ______ 

Options

• `51/140`

• `9/170`

• `9/70`

• `51/70`

Answer 1

There are two bags. One bag contains 4 blue pens and 3 black pens. The other bag contains 7 red pens and 3 black pens. If a bag is selected at random and from it, a pen is drawn, the probability that the pen is black is `underline(51/140)`.

Explanation:

The probability of selecting a bag is `1/2`.

In the first bag, there are 3 black pens out of 7, and in the second box, there are 3 black pens out of 10.

∴ Required probability = `1/2 xx 3/7 + 1/2 xx 3/10`

= `51/140`