Can I get the question please. I might help you with your question.
An irrational number/value is one you cannot express in terms of a ration, or a fraction, it cannot be written as fraction
now 291.87... is simple, two decimals, so you use two zeros at the botom and end up with

and boom, there you are, a fraction, nice and dandy
now, let's see the first one -√(127) well, low and behold, 127 is a prime number, and and thus is has no two factors that'd serve as root, so, there's no rational root that'd give that, that makes it irrational
Let three consecutive multiples of 7 be 7x,7x+7 and 7x+14
We are given that there are a total of 78 students. If we set the following variables:

Then, the sum of all of these must be 78, that is:

Since there are 15 in chemistry and physics and 47 in chemistry, we may replace that into the equation and we get:

Simplifying:

Now we solve for P by subtracting 62 on both sides:

Therefore, there are 16 students in physics