Question Details

Given that π‘Ž and 𝑏 are integers and π‘Ž + π‘Ž 2𝑏 3 is odd, which one of the following statements is correct?

Options

A

π‘Ž and 𝑏 are both odd

B

π‘Ž and 𝑏 are both even

C

π‘Ž is even and 𝑏 is odd

D

π‘Ž is odd and 𝑏 is even

Correct Answer :

π‘Ž is odd and 𝑏 is even

Solution :

The correct option is: π‘Ž is odd and 𝑏 is even.

To understand why this is the correct statement, let us analyze the given mathematical expression:

a + a 2 b 3

We are given that this expression evaluates to an odd integer. We can simplify the analysis by factoring out the term a from the expression:

a ( 1 + a b 3 )

For the product of two integers to be odd, both factors must be odd. Therefore, we can establish two conditions that must be satisfied simultaneously:

1. The first factor, a, must be odd.

2. The second factor, 1+ab3, must also be odd.

Now, let us examine the second condition. If the sum 1+ab3 is odd, then the term ab3 must be even (since an odd number minus 1 is even). Therefore:

a b 3 is even

We already determined from the first condition that a is odd. For the product of two integers a and b3 to be even, at least one of them must be even. Since a is odd, it must be that b3 is even.

Finally, since the cube of an integer preserves its parity (the cube of an odd integer is odd, and the cube of an even integer is even), b3 being even implies that b must be even.

Thus, we have shown that a is odd and b is even.

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