probability of fewer than 4 failures in 100 launches

G

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A certain type of rocket has a failure rate of 1.5%.

Use the methods developed in this section to determine the probability of fewer than 4 failures in 100 launches.

Now how do you do FEWER questions? Because I tried doing:

100C0 ( .015) ^ 0 ( 1-0.15)^100....+100C3 (.015)^3(0.985)^97= .71

But the answer is .9358, so I guess Im wrong on how to do questions when they say FEWER THAN.
So how do you do them?

Thanks for the help =)
 
Looks like you're doing it right. Just got bad calculations.

Use k=0 to 3.

\(\displaystyle \L\\\displaystyle\sum_{k=0}^{3}C(100,k)(0.015)^{k}(0.985)^{100-k}\)
 
It's called binomial probability. The formula in the first reply is correct - it's simply the lower cumulative binomial distribution probability. More details and easy online calculation of this probability is here.
 
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