 Welcome to our session. Let us discuss the following question. The question says which room of the AP51321 is 181? Now begin with the solution. Let APB181 P is 53021 and so on. Term that is A is equal to 5 and common difference that is D is equal to 13 minus 5 that is 8. AP is 181 so we have 181 equals to A is 5, 81 minus 5 is equal to N minus 1 into D. Now 181 minus 5 is 1, 7 into A and this implies 2 is equal to N minus 1.