Ten years ago, average of the ages of a men and his wife was 25 years. Today the average age of these two and their son, taken together is again 25 years. What is the age (in years) of the son today?

Ten years ago, the average age of the man and his wife was 25, meaning their total age was 2 multiplied by 25, or 50 years. Today, their combined age has increased by 2 times 10 years, making it 70 years. With the son included, the average age of the 3 people today is 25, so their total age is 3 multiplied by 25, or 75 years. The son's age is the difference between 75 and 70, which is 5 years.

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