The Netflix prize competition started in October 2006. Training data is ratings for 18,000 movies by 400,000 Netflix customers, each rating between 1 and 5. Training data is very sparse about 98% missing. Objective is to predict the rating for a set of 1 million customer-movie pairs that are missing in the training data. Netflix's original algorithm achieved a root MSE of 0.953. The first team to achieve a 10% improvement wins one million dollars.

a. Is this a regression or classification problem? and why?

b. Is this a supervised or unsupervised problem? and why?