Check If Answer for a Question is Correct by Similarity
This problem can be solved better if you also include the background text from where the questions have been picked up. Then, firstly train word embeddings on the background text. Further, generate sentence compositionality of the questions as well as their answers using a Recursive Neural Network or some variant. After all these steps you can compute the similarity between compositions of the new answer and given answers to know if it is correct or not.