PSLE
In a school hall, chairs were arranged in rows such that there were exactly 35 chairs in each row. For a concert, Valen removed 4 chairs from the school hall and rearranged all the chairs. There are now exactly 8 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	35	8
Total value	35 u - 4	8 u + 104

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

Number of chairs at first after the 4 chairs were removed
= 35 x 1 u - 4
= 35 u - 4

Number of chairs in the end
= 8 x (1 u + 13)
= 8 u + 104

The total number of chairs is equal.

35 u - 4 = 8 u + 104
35 u - 8 u = 104 + 4 
27 u = 108

1 u = 108 ÷ 27 = 4 

Number of chairs in the end
= 8 u + 104
= 8 x 4 + 104
= 136

Answer(s): 136