There are five odd numbers 1, 3, 5, 7 and 9. What is the HCF of these odd numbers?

• A. 2
• B. 1
• C. 6
• D. 3

The highest common factor (HCF) of a set of numbers is the largest number that divides all of them without leaving a remainder. In the case of the odd numbers 1, 3, 5, 7, and 9, we need to find the HCF among them.

Analyzing the Numbers

Let's look at the factors of each number:

• Factors of 1: 1
• Factors of 3: 1, 3
• Factors of 5: 1, 5
• Factors of 7: 1, 7
• Factors of 9: 1, 3, 9

Finding the Common Factor

The only factor that appears in all these lists is 1. Therefore, the highest common factor of the numbers 1, 3, 5, 7, and 9 is:

Final Answer

1

Thus, the correct option is B. 1.