Andy claims that his bird can do single-digit multiplication. He shows the bird 12 cards with simple multiplication problems that are either correct or incorrect. The bird correctly identifies the correctness of the card 9 times out of 12. If the bird were simply guessing, how many would the bird be expected to get correct?

3

9

6

12

Question

Andy claims that his bird can do single-digit multiplication. He shows the bird 12 cards with simple multiplication problems that are either correct or incorrect. The bird correctly identifies the correctness of the card 9 times out of 12. If the bird were simply guessing, how many would the bird be expected to get correct?

 3

 9

 6

 12

anonymous · Answer

If the bird were just guessing there would be two options (right or wrong) and we would expect them to be equally likely to occur (50% chance for each).  A 50% of correct, out of 12 cards gives us:$$12 \times 0.50= 6$$. 

If the bird was guessing we would expect 6 correct answers. (1/2 of the total correct and 1/2 wrong.)   Answer: C