You save $5 per chair with the 25% off sale.
On sale chairs cost $15 each because 20 - 5 = <<20-5=15>>15
You bought 3 chairs above the 5 required before the extra savings starts because 8 - 5 = <<8-5=3>>3
You save an extra $5 on these chairs because 15 x (1/3) = <<15*(1/3)=5>>5
The first five chairs cost $75 in total because 5 x 15 = <<5*15=75>>75
The final three chairs cost $30 in total because 3 x 10 = <<3*10=30>>30
In total they cost $105 because 75 + 30 = <<75+30=105>>105
#### 105