0.5,
are rational. √24, 3.42859873 are irrational.
Solution:
Rational numbers can be expressed as
form.
Option A: 0.5

It is of the form
.
Therefore 0.5 is a rational number.
Option B:



It cannot be simplified further. Roots are irrationals.
Therefore √24 is irrational.
Option C: 3.42859873
It cannot be written as
form.
Therefore 3.42859873 is irrational.
Option D:

It is of the form
.
Therefore
is rational.