The owner of a local electronic store is checking the quality of toasters sold at his shop. He knows that out of 20, three toasters might have faulty timer knobs, which may fall off. He randomly selects five toasters for testing. Compute the probability for

a. all the toasters’ timer knobs falling off.

b. none of the toasters’ timer knobs falling off.

c. more than half of the toasters’ timer knobs falling off.