In this question we can see that it is actually the addition of fractional numbers. The addition should be done carefully. Now let us get down to the addition part.
Total number of books i had = (1/8) + (1/5)
= (5 + 8)/40
= 13/40
So the total number of books that i had was 13/40. I hope this is the answer you were looking for. Although the result seems a bit awkward, but still this is the correct result. Hopefully the procedure is clear enough for you understand. In future you can always use this procedure for solving similar type of problems.