Questionnaire on Probability in statistics

A Problem in Statistics is given to three students A, B and C whose chances of solving it are.

What is the probability that the problem will be solved if all of them try independently?

In a bolt factory, machines A, B and C manufacture 25%, 35% and 40% respectively of the total. Of their output 5, 4, 2 per cent are defective bolts. A bolt is drawn at random from the product and is found to be defective. What are the probabilities that it was manufactured  by machines A, B and C?