1 00:00:00,600 --> 00:00:01,940 Now let's do an example. 2 00:00:01,940 --> 00:00:06,740 So here's your reminder of the formula and suppose this is my data. 3 00:00:06,740 --> 00:00:11,040 I have four data points and for each data point I have three features, 4 00:00:11,040 --> 00:00:17,570 the grade of the train, the bumpiness, whether there's a speed limit, 5 00:00:17,570 --> 00:00:20,709 and then the speed that the car goes. 6 00:00:21,950 --> 00:00:23,440 And i'm just making up some data here. 7 00:00:23,440 --> 00:00:26,890 So let's start out at the top of the decision tree here. 8 00:00:26,890 --> 00:00:31,960 So I have two slow examples and two fast examples. 9 00:00:31,960 --> 00:00:36,200 Slow, slow, fast, fast. 10 00:00:36,200 --> 00:00:39,199 So the first question is, what's the entropy of this node? 11 00:00:40,470 --> 00:00:42,590 So let's do this piece by piece. 12 00:00:42,590 --> 00:00:46,880 How many of the examples in this node are slow? 13 00:00:46,880 --> 00:00:47,810 Write your answer here.