He estimates the building on the left is 80 feet tall because 100 x .8 = <<100*.8=80>>80

The combined height of the left and middle is 180 because 100 + 80 = <<100+80=180>>180

The building on the right he estimates as 160 feet because 180 - 20 = <<180-20=160>>160

He estimates the combined height as 340 feet because 80 + 100 + 160 = <<80+100+160=340>>340

# Answer

340
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Quinten sees three buildings downtown and decides to estimate their heights. He knows from a book on local buildings that the one in the middle is 100 feet tall. The one on the left looks like it is 80% of the height of the middle one. The one on the right looks 20 feet shorter than if the building on the left and middle were stacked on top of each other. How tall does Quinten estimate their total height to be?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
340
Quinten sees three buildings downtown and decides to estimate their heights. He knows from a book on local buildings that the one in the middle is 100 feet tall. The one on the left looks like it is 80% of the height of the middle one. The one on the right looks 20 feet shorter than if the building on the left and middle were stacked on top of each other. How tall does Quinten estimate their total height to be?
train