A) because the decimal is repeating, 625.49 is irrational.
B) because 625.89 can be written as the ratio of two integers, 62589 and 100000, this is a rational number.
C) sqrt(90) can be factored: sqrt(9)*sqrt(10). sqrt(9) = 3 (rational), but sqrt(10) is irrational. Thus sqrt(90) is irrational.
D) You try this one yourself, OK?
