Take any two odd numbers. Find their product. Is the product an odd number? Repeat observations for 3 more pairs of odd numbers. What do you conclude?
The correct answer and explanation is:
Correct Answer:
Yes, the product of two odd numbers is always an odd number.
Observations:
- 3 × 5 = 15 → odd
- 7 × 9 = 63 → odd
- 11 × 13 = 143 → odd
- 15 × 17 = 255 → odd
Explanation:
An odd number is a number that is not divisible by 2. It can be written in the general form of 2n + 1, where n is any integer.
When two odd numbers are multiplied, the expression looks like this:
(2a + 1) × (2b + 1), where a and b are integers.
Let us expand this:
(2a + 1)(2b + 1)
= 2a × 2b + 2a × 1 + 1 × 2b + 1 × 1
= 4ab + 2a + 2b + 1
= 2(2ab + a + b) + 1
This final expression is in the form of 2k + 1, where k = 2ab + a + b, which is an integer. Therefore, the product is also an odd number.
In all the examples tried above, the product of each pair of odd numbers resulted in an odd number. This consistent outcome confirms the general rule that the product of two odd numbers is always odd.
The reason this holds true is because odd numbers have a remainder of 1 when divided by 2. When two such numbers are multiplied, the result retains that same basic structure, ending in an odd digit, and never becoming divisible by 2.
Conclusion:
The product of two odd numbers is always an odd number. This is supported by both algebraic proof and numerical examples.