(Decision tree)

Entropy=

-268/768 * log2(268/768) - 500/768 * log2(500/768) = 0.918

Information gain=

Age < 30: Entropy = -20/100 * log2(20/100) - 80/100 * log2(80/100) = 0.72

30 <= Age < 60: Entropy = -80/300 * log2(80/300) - 220/300 * log2(220/300) = 0.69

Age >= 60: Entropy = -168/368 * log2(168/368) - 200/368 * log2(200/368) = 0.95

Entropy(after split) = (100/768) * 0.72 + (300/768) * 0.69 + (368/768) * 0.95 = 0.86

Information Gain(Age) = Entropy(before split) - Entropy(after split) = 0.918 - 0.86 = 0.058

________________________________________________________________

From this information Write an introduction about the Gini index and calculate it.