In a row, a student is standing 13th from the right and 8th from the left. How many students are there in total?

Since there is student whose number is 13th from the right side and the same student has number 8th from the left, so in both the case the student is common.
Hence the calculation should be like this:
12+1=13
7+1=8
since 1 is common in both the case
hence,
we add:
12+7+1=20
hence there are total 20 students standing in a row.