We can interpret the sum 3/4+1/6 as representing the fraction of a single pie we would have if we combined 3/4 of a pie with 1/6 of an equal-sized pie. Explain why we must give the two fractions a common denominator in order to compute the sum 34+16. (Do not just explain the procedure for adding the two fractions. Try to explain the reasoning behind why we follow that procedure.)
Explanation should be very clear and easy to understand so that an elementary student would be able to understand the answer.