PSLE
In a school hall, chairs were arranged in rows such that there were exactly 23 chairs in each row. For a concert, George removed 5 chairs from the school hall and rearranged all the chairs. There are now exactly 15 chairs in each row and 13 more rows than before. How many chairs are there in the school hall for the concert in the end?

	Before	After
Number	1 u	1 u + 13
Value	23	15
Total value	23 u - 5	15 u + 195

Number of rows at first = 1 u
Number of rows in the end = 1 u + 13

Number of chairs at first after the 5 chairs were removed
= 23 x 1 u - 5
= 23 u - 5

Number of chairs in the end
= 15 x (1 u + 13)
= 15 u + 195

The total number of chairs is equal.

23 u - 5 = 15 u + 195
23 u - 15 u = 195 + 5 
8 u = 200

1 u = 200 ÷ 8 = 25 

Number of chairs in the end
= 15 u + 195
= 15 x 25 + 195
= 570

Answer(s): 570