The number of errors in a textbook follow a poisson distribution with a mean of 0.01 errors per page. what is the probability that there are 3 or less errors in 100 pages? round your answer to four decimal places (e. g. 98.7654).

Mean number of errors in each page = 0.01
Mean number of errors in 100 pages = 0.01*100=1

It is possible to use the cumulative distribution function (CMF), but the math is a little more complex, involving the gamma-function.  Tables and software are available for that purpose.

Thus it is easier to evaluate with a calculator for the individual cases of k=0,1,2 and 3.

The Poisson distribution has a PMF (probability mass function) 

with λ = 1
=>




=>

or
P(k<=3)=0.9810 (to four decimal places)