Suppose on performing reduced error pruning, we collapsed a node and observed an improvement in the prediction accuracy on the validation set.
Which among the following statements are possible in light of the performance improvement observed?
(a) The collapsed node helped overcome the effect of one or more noise affected data points in the training set
(b) The validation set had one or more noise affected data points in the region corresponding to the collapsed node
(c) The validation set did not have any data points along at least one of the collapsed branches
(d) The validation set did have data points adversely affected by the collapsed node

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• Having built a decision tree, we are using reduced error pruning to reduce the size of the tree. We select a node to collapse. For this particular node, on the left branch, there are 3 training data points with the following outputs: 5, 7, 9.6 and for the right branch, there are four training data points with the following outputs: 8.7, 9.8, 10.5, 11. What were the original responses for data points along the two branches (left & right respectively) and what is the new response after collapsing the node?
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