Answer:
John is
20
Mary
12
Explanation:
We can use one variable to define their ages because we know the relationship between their ages.
Mary is younger, let Mary's present age be
x
years,
Then John's present age is
32
−
x
years (Sum of their ages is
32
)
4
years ago, they were both
4
years younger than now.
Mary was
(
x
−
4
)
and John was
(
32
−
x
−
4
)
=
(
28
−
x
)
years old.
John was twice as old as Mary:
2
(
x
−
4
)
=
28
−
x
2
x
−
8
=
28
−
x
3
x
=
28
+
8
3
x
=
36
x
=
12
Mary's age is
12
and John's age is
20