Question 1150170
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            I will solve the problem in two steps.

            Watch my steps.


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(1)  From the condition,


        Sam + Tony = 36

        Sam - Tony =  4


    Add the equations. You will get  


        2*Sam = 40,   Sam = 20.


    Hence, Tony is 16 years old.


(2)  Three years ago, the sum of ages Mark + Tony was  33 years.

     Hence, currently it is  33+3+3 = 39 years:


         Mark + Tony = 39,   or

         Mark + 16 = 39.


     Hence, Mark = 39-16 = 23.


<U>ANSWER</U>.  Mark is 23 years old; Tony is 16 years old;  Sam is 20 years old.
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Solved.