Question

Critical Thinking Explain why all two-digit whole numbers with 5 as the ones’ digit are composite.

Short answer

All two-digit whole numbers with 5 as the one’s digit will always have 5 as one of the factors apart from 1 and itself and therefore, will be a composite number.

Step-by-step solution

  Define composite numbers and prime numbers

Composite numbers are defined as whole numbers that has more than 2 factors and prime numbers are defined as whole numbers that is greater than 1 and has exactly two whole number factors 1 and itself.

  Observe two-digit whole numbers with 5

Every multiple of 5 is a composite number except for the number 5 itself.

For instance, let’s take 25. Now, the number is divisible by 5. Hence, the number is composite.

Let’s take another example 75. Here too the number is divisible by 5 hence, is not a prime number thereby being a composite.

  State the conclusion

Since, both the numbers have more than two factors, therefore they are composite numbers and by this it can be concluded that all the two-digit numbers with ones’ digit as 5 are composite numbers.