Answer:
A
Step-by-step explanation:
You find the mean by adding all the values then dividing that sum by the amount of values
You find the median by putting the numbers in order from least to greatest and then find the middle number.
If the series is made up of numbers in an arithmetic progression, you have

where

is the first term and

is the common difference between terms.
Since the last term in the series is

, you have

Solve the system

and you'll find that the first term is

(with

).
In mathematics, the irrational numbers are all the real numbers which are not rational numbers, the latter being the numbers constructed from ratios (or fractions) of integers.