PSLE
In a school hall, chairs were arranged in rows such that there were exactly 29 chairs in each row. For a concert, Henry removed 4 chairs from the school hall and rearranged all the chairs. There are now exactly 12 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	29	12
Total value	29 u - 4	12 u + 132

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 removed
= 29 x 1 u - 4
= 29 u - 4

Number of chairs in the end
= 12 x (1 u + 11)
= 12 u + 132

The total number of chairs is equal.

29 u - 4 = 12 u + 132
29 u - 12 u = 132 + 4 
17 u = 136

1 u = 136 ÷ 17 = 8 

Number of chairs in the end
= 12 u + 132
= 12 x 8 + 132
= 228

Answer(s): 228