irrational numbers are number that can't be written in a/b form where a and b are integers and b≠0
if it repeats, it can be written as a fraction
if it terminates, it can also be written as a fraction
if you have a square root that doesn't simplify nicely, we assume it to be irrational
so
A. 0.454545=45/99
B. irrational
C. 7/9
D. 3/10
yep, it's √5
