Johns-mom-is-older-than-John-by-twenty-years-old-Twenty-years-later-how-old-is-Johns-mother-older-than-twenty-years-laters-John

If we let "J" be John's current age, then his mother's age is J+20.

In twenty years, John's age will be J+20, and his mother's age will be J+20+20 = J+40.

Therefore, John's mother will be (J+40) - (J+20) = 20 years older than John twenty years later.