Question 1161201
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The common difference for the first AP is  4;  for the second AP  is  7.


The common terms form an AP with the first term 1 and the common difference equal to


    28 = 4*7 = Least Common Multiple of 4 and 7 = LCM(4,7).


Hence, the first three common terms are  1, 29, 57.


Their sum is  1 + 29 + 57 = 87.     <U>ANSWER</U>
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Solved.