Question

Which of these numbers is irrational? A. 12 B. -4.2 C. 1/42 D. 4.2

Answer 1

Answer:

A: 12

Step-by-step explanation:

An Irrational Number is a real number that cannot be written as a simple fraction.  (Irrational means not rational).

Therefore, we can immediately discount C as 1/42 is a rational number by inspection.

$4.2=\frac{4.2}{1} =\frac{4.2}{1} \times \frac{10}{10} =\frac{42}{10}=\frac{21}{5}$  so  similarly -4.2 = -21/5

So as B and D can also be written as rationals, they are not irrational.

Therefore, A is irrational.