At present Mary is 4 years younger than Peter. If Peter is n years old, what will be the sum of their ages in three years time?

If Mary is 4 years younger than Peter, then Mary's age can be represented as n - 4.

In three years time, Peter will be n + 3 years old and Mary will be (n - 4) + 3 = n - 1 years old.

Therefore, the sum of their ages in three years time will be (n + 3) + (n - 1) = 2n + 2 years.

Mary's present age = (n - 4) years
Peter's present age = n years
Mary's age after 3 years = (n - 4) + 3 = (n - 1) years
Peter's age after 3 years = n + 3 years
Therefore, the sum of their ages in three years time = (n - 1) + (n + 3) = 2n + 2 years

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