Question

Select a counter-example that makes the conclusion false.. . You select three marbles from a bag and each of them is black.. . Conclusion: All the marbles in the bag are black.. . Counterexample:

Answer 1

Counterexample : You select three marbles from a bag and at least one of them is not black

Explanation:

Counterexample is referred to as an example that contradicts or opposes an idea or theory.

So, in this case to find a counterexample, we need to find an example that opposes or makes the conclusion false. The conclusion is : All the marbles in the bag are black so we need an example that shows atleast one marble is not black.

So, we choose the required counterexample as " You select three marbles from the bag and atleast one of them is not black"

Answer 2

We must select a counter example that makes the conclusion false. Say that 3 is a prime number, 5 is a prime number, and 7 is a prime number.

The conclusion is all odd numbers are prime

a counterexample is 9 is an odd number but it is also not a prime number.