There are 10 rows of 15 chairs set up for the award ceremony. The first row is reserved for the awardees while the second and third rows are for the administrators and teachers. The last two rows are then reserved for the parents and the rest of the rows are for the students. If only 4/5 of the seats reserved for the students are occupied, how many vacant seats from the students can be given to the parents? Let's think first. Chain of thought:
There are 1 + 2 + 2 = 5 rows that are not reserved for the students. Hence, 10 - 5 = 5 rows are reserved for the students. That is equal to 5 x 15 = 75 seats. But only 75 x 4 / 5 = 60 seats are occupied by the students. Therefore, 75 - 60 = 15 seats can be given to the parents.
Therefore, the answer is 15.