Question

He probability of a bomb hitting a bridge is 1/2 and twodirect hits are neede to destroy it.The least no of bombs required so that the probability of the bridge being destroyed is greater than 0.9 is?

Answer 1

Thank you for asking this question. Here is your answer:

The probability of the bridge being destroyed is greater than 0.9 that means  probability of the bridge being not destroyed is lesser than 0.1 .

We will let n bombs are needed

Now we will find all probabilities of the bridge being not destroyed by binomial distribution i.e.

[nC0+nC1]*(0.5)^n < 0.1

Now we will examine it for values n = 1,2,3,4,,....

You will see that n = 1 to 6

The above inequality doesn't satisfy

It first time satisfies for n = 7

So the final answer for this question is 7

If there is any confusion please leave a comment below.