###Human: In four years, Peter will be twice as old as Harriet. If Peter's age is currently half of his mother's age, who is 60, how old is Harriet now?, ### Assistant: If Peter's age is currently half of his mother's age, who is 60, Peter is 1/2*60 = 30 years old.
In four years, Peter will be 30+4 = 34 years old.
Since Peter's age in four years will be twice Harriet's age, Harriet will be 34/2 = 17 years old in four years.
Currently, Harriet is 17-4 = 13 years old. 
 So the answer is :  13