# Math Help - no. of bombs required to destroy : question

1. ## no. of bombs required to destroy : question

please give me a clue for the following question..

There is 50% chance that any bomb may hit the target. Two direct hits are required to destroy the target completely. How many bombs must be dropped for 99% chance?

2. ## Re: no. of bombs required to destroy : question

Originally Posted by electroboy
please give me a clue for the following question..

There is 50% chance that any bomb may hit the target. Two direct hits are required to destroy the target completely. How many bombs must be dropped for 99% chance?

$1-\sum_{k=0}^{1} \binom{n}{k}\ p^{k}\ (1-p)^{n-k} = .99$ (1)
... where $p=\frac{1}{2}$ and $n$ is the 'unknown quantity'...
$\chi$ $\sigma$