In this case we add the second premise. So the premises we consider are No Stars are moons “and” All balls are moons.
When we consider all the three premises together that is Some bats are balls “,” No Stars are moons “and” All balls are moons we can arrive at all the below Euler Diagrams. To make it clear, case 1 - A represents that bats intersects only the balls that is a bat cannot be moon without also being a ball. Similarly you can understand all the remaining cases.
Now we add bats to the Case 2 and come up with following diagrams. Here Case 2 - A represents a scenario in which bats, moons and balls overlap.
Now lets consider the conclusions one by one. Note that for a conclusion to be absolutely true it must be true with all the above Euler Diagrams. That is to make the conclusion false, we need to find only a single Euler Diagram (derived from the premises) which invalidates it.
Conclusions:
Therefore conclusion 2 and 4 are correct.
Now in general to solve these questions really quickly, we would start start from the conclusions and for each conclusion we will try to come up with a single possibility (from the premises) which invalidates that conclusion. A conclusion is true if there is no possibility which can invalidate it.
✍Examrace Team at Aug 23, 2021