Well, a rational decimal is like a simple 3.1 or 4.5. It just cuts off easily. Another example would be a repeating decimal like 3.333333...
An irrational decimal is like 3.1415682983523576294875 with no pattern or cutoff point.
Sorry if I am wrong.
2n+5...a couple is two people so you need to multiply the number of couples, n, by 2 to get the total number of dancers. Then add the total number of organizers.
They are equal because you can measure the percentage as a decimal with a maximum of 1.
They lie in the same plane is the answer ;)