Is 0.6666 an irrational number

NO!!!

As given it is a terminating decimal, and as a fraction it is 6666/10000

However,as a recurring decimal to infinity, it can be converted to a ratio/fraction .

Hence

Let P = 0.66666....

10P = 6.66666....

Subtract

9P = 6.0 (Note the recurring decimal subtract to 'zero'.

Hence

9P = 6

P = 6/9

Cancel down by '3'

P = 2/3

NB Resurring decimals to infinity are written as 0.666... ( Note the three or more dots. This indicates to mathematicians, that it recurs to infinity, otherwise it is a terminating decimal.

NNB Irrational Numbers are those that recur to inifinity AND the decimal digits are not in any regular order. . 'pi' 3.141592.... being the most well known irrational number.