John is half times his father's age.

Thus 1/2*40 = <<1/2*40=20>>20 years.

Since the mother is 4 years younger than the father, she is 40-4= <<40-4=36>>36 years old.

The age difference between John and his mother is 36-20 = <<36-20=16>>16 years

# Answer

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John is half times younger than his father, who is 4 years older than John's mother. If John's father is 40 years old, what's the age difference between John and his mother?
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16
John is half times younger than his father, who is 4 years older than John's mother. If John's father is 40 years old, what's the age difference between John and his mother?
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