Why did gerrit rietveld use lumber cut in standard size for his red-blue chair?

He had hoped his chair(s) would go on to be mass-produced, not hand-crafted. As a matter of fact, he had hopes that much of his furniture would be mass-produced--he aimed for simplicity in construction. The pieces of wood that comprised the Red Blue Chair were the standard lumber sizes readily available at the time.

if you are a plato/edmentum user this is the answer

1. eadweard muybridge creates series photography - 1877

2. the kinetograph - 1889

3. philo farnsworth - 1929

4. kodak introduces kodachrome - 1935

5.   once upon a time in mexico was the first film to be shot digitally - 2003

i hope this ! : )