PSLE
In a school hall, chairs were arranged in rows such that there were exactly 17 chairs in each row. For a concert, Seth brought 4 more chairs into the school hall and rearranged all the chairs. There are now exactly 14 chairs in each row and 11 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 + 11
Value	17	14
Total value	17 u + 4	14 u + 154

Number of rows at first = 1 u
Number of rows in the end = 1 u + 11

Number of chairs at first after the 4 chairs were brought in
= 17 x 1 u + 4
= 17 u + 4

Number of chairs in the end
= 14 x (1 u + 11)
= 14 u + 154

The total number of chairs is equal.

17 u + 4 = 14 u + 154
17 u - 14 u = 154 - 4 
3 u = 150

1 u = 150 ÷ 3 = 50 

Number of chairs in the end
= 14 u + 154
= 14 x 50 + 154
= 854

Answer(s): 854