Betty's daughter is 40/100 * 60 = <<40/100*60=24>>24 years younger than she is.

That means her daughter is 60 - 24 = <<60-24=36>>36 years old.

So the granddaughter is 1/3 * 36 = <<1/3*36=12>>12 years old.

# Answer

12
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
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?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
12
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?
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