Question

Which of the following real numbers are classified as natural numbers

Answer 1

Natural numbers:

The natural numbers are the positive integers (whole numbers) starting from 1.

`\N=\mleft\lbrace1,2,3,4,5\ldots\mright\rbrace`

Note that natural numbers are never negative or fraction/decimal.

Let us analyze the given options and identify the natural numbers.

1st option: √32

This is an irrational number and hence not a natural number,

2nd option: 4/28

As you can see this is not a whole number since it is in fraction.

Therefore, it is not a natural number.

3rd option: -√49

As you can see it is a negative integer and we know that natural numbers are never negative.

Therefore, it is not a natural number.

4th option: √81

Notice that the square root of 81 is 9 that is a positive integer. (whole number)

`\sqrt[]{81}=9`

Therefore, it is a natural number.

5th option: 28/4

Notice that 28/4 can be simplified to 7 that is a positive integer (whole number)

Therefore, it is a natural number.

6th option: -15

As you can see it is a negative integer and we know that natural numbers are never negative.

Therefore, it is not a natural number.

Hence, only 4th and 5th options are natural numbers.