[Question]: A school has 15 classrooms. One-third of these classrooms have 30 desks in each classroom and the rest have 25 desks in each classroom. Only one student can sit at one desk. How many students can this school accommodate so that everyone has their own desk?
[Answer]: One - third of the classrooms have 30 desks, so there are 1 / 3 * 15 = 5 classrooms like that. The rest, which means 15 - 5 = 10 classrooms, have 25 desks. One - third of the classrooms can fit 5 * 30 = 150 students. The rest can fit 10 * 25 = 250 students. So in total, the school can be filled with 150 + 250 = 400 students.
So the answer is 400.

[Question]: A concert ticket costs $40. Mr. Benson bought 12 tickets and received a 5% discount for every ticket bought that exceeds 10. How much did Mr. Benson pay in all?
[Answer]: Mr. Benson had a 5% discount for each of the 12 - 10 = 2 tickets. So, those two tickets had a $40 x 5 / 100 = $2 discount each. Hence, each ticket cost $40 - $2 = $38 each. Thus, two discounted tickets amount to $38 x 2 = $76. And the other ten tickets amount to $40 x 10 = $400. Hence, Mr. Benson paid a total of $400 + $76 = $476.
So the answer is 476.

[Question]: Bernie has a collection of 18 unique postcards. He decided to sell half his collection for $15 per postcard. After he has successfully sold his postcards he decided to spend all the earned money to buy new postcards for $5 each. How many postcards does Bernie have after all his transactions?
[Answer]:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Half of Bernie's collection means 18 * 0.5 = 9 postcards. So he was able to sell 9 postcards for 9 * 15 = $135. He decided to spend all of his money on new postcards for $5 each, so he was able to buy 135 / 5 = 27 new postcards. This means Bernie has 9 + 27 = 36 postcards after all.
So the answer is 36.