Question 1202102
<pre>
To have won two prizes in n trials is the same as failing to win fewer than n-2
times in n trials.

By my TI-84, binomcdf(21,0.8,19) gives 0.9423539248 which is not quite 0.95

but binomcdf(22,0.8,20) gives 0.9520384654

So the answer is 22.

Edwin</pre>