There was an equal number of chairs and desks in the morning. At 4 p.m., some chairs were added and some desks were removed, resulting in the number of chairs being increased by 20% while the number of desks decreased by 30%. At 9 p.m. the number of chairs increased by 50%. If a total of 40 chairs were added during the day, how many more chairs than desks were there in the end?

At 4 p.m.	Chairs	Desks
Before	1 u	1 u
Change	+ 0.2 u	- 0.3 u
After	1.2 u	0.7 u

At 9 p.m.	Chairs	Desks
Before	1.2 u	0.7 u
Change	+ 0.6 u	No change
After	1.8 u	0.7 u

Number of chairs added
= 20% x 1 u
= ²⁰₁₀₀ x 1 u
= 0.2 u

Number of desks removed
= 30% x 1 u 
= ³⁰₁₀₀ x 1 u
= 0.3 u

Number of chairs increased by chairs at 9 p.m.
= 50% x 1.2 u
= ⁵⁰₁₀₀ x 1.2 u
= 0.6 u

Number of chairs added during the day
= 1.8 u - 1 u
= 0.8 u

0.8 u = 40

1 u = 40 ÷ 0.8 = 50

Number of more chairs than desks in the end
= 1.8 u - 0.7 u
= 1.1 u
= 1.1 x 50
= 55

Answer(s): 55