Final answer:
Johnny's claim that 1/3 is an irrational number is incorrect because 1/3, with its repeating decimal 0.3333333, is in fact a rational number as it can be written as a fraction of two integers.
Step-by-step explanation:
Johnny is incorrect in his statement that 1/3 is an irrational number because it repeats forever as 0.3333333. In fact, the truth is exactly the opposite. Rational numbers are defined as numbers that can be expressed as a fraction of two integers, and they may either terminate or repeat after the decimal point. In the case of 1/3, it is indeed a rational number because it can be expressed as a quotient of two integers (1 divided by 3), and the decimal expansion is repeating rather than non-repeating and non-terminating, which would characterize an irrational number.
Therefore, the correct statement is C: Johnny is incorrect because a repeating decimal is rational. Terminating or repeating decimals always represent rational numbers, since they can be converted into fractions where both the numerator and denominator are integers. For instance, the repeating decimal 0.3333333 can be represented as the fraction 1/3.