Answer:
There is a 99.99998% probability that at least one valve opens.
Step-by-step explanation:
For each valve there are only two possible outcomes. Either it opens on demand, or it does not. This means that we use the binomial probability distribution to solve this problem.
Binomial probability distribution
The binomial probability is the probability of exactly x successes on n repeated trials, and X can only have two outcomes.

In which
is the number of different combinatios of x objects from a set of n elements, given by the following formula.

And p is the probability of X happening.
In this problem we have that:

Calculate P(at least one valve opens).
This is 
Either no valves open, or at least one does. The sum of the probabilities of these events is decimal 1. So:


So


Finally

There is a 99.99998% probability that at least one valve opens.
A factor of 30 is chosen at random. What is the probability, as a decimal, that it is a 2-digit number?
The positive whole-number factors of 30 are:
1, 2, 3, 5, 6, 10, 15 and 30.
So, there are 8 of them. Of these, 3 have two digits. Writing each factor on a slip of paper, then putting the slips into a hat, and finally choosing one without looking, get that
P(factor of 30 chosen is a 2-digit number) = number of two-digit factors ÷ number of factors
=38=3×.125=.375
Acute angles because they are less then 90 degrees which is a right angle.