<human>:  The length of the straight part of a river is three times shorter than the crooked part. If the river is 80 miles long, how long is the straight part of the river?
<bot>: Define a variable ** Let's say the river's length in the straight part of the river is x.
Write an equation ** The total length of the river is the length of the straight part plus 3 times the length of the straight part for the crooked part, which is x+3x = 80
Combine like terms ** The total length of the river is 4x=80
How long is the straight part of the river? ** The straight part of the river is x=80/4 = <<80/4=20>>20 miles.
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