Betty is 60 years old, and she is the oldest person in the family. Her daughter is 40 percent younger than she is, and her granddaughter is one-third her mother's age. How old is the granddaughter? Think carefully first, then make a decision:
Betty's daughter is 40 / 100 * 60 = 24 years younger than she is. That means her daughter is 60 - 24 = 36 years old. So the granddaughter is 1 / 3 * 36 = 12 years old. So, the answer is 12.