To find the sum of 7 8/10 and 7 9/10, we can first add the whole numbers, which are 7 and 7. This gives us a sum of 14. Next, we add the fractions separately. For the fractions 8/10 and 9/10, we need to have a common denominator to add them together. Since both fractions have a denominator of 10, we can add the numerators directly. Adding 8 and 9 gives us 17. Finally, we combine the whole number sum of 14 with the fraction sum of 17/10. To do this, we convert the fraction 17/10 into a mixed number. Since the denominator 10 can be divided evenly into 17, we can write it as 1 and 7/10. Adding 14 and 1 gives us a final answer of 15, and adding 7/10 and 7/10 gives us a final fraction of 14/10. Therefore, the sum of 7 8/10 and 7 9/10 is 15 14/10.