The chickens cost $80 because 4 x 20 = <<4*20=80>>80

His chickens produce a dozen eggs a week because 4 x 3 = <<4*3=12>>12

Each week that he has chickens is $1 cheaper than buying eggs because 2 - 1 = <<2-1=1>>1

After 80 weeks his chickens will be paid off because 80 / 1 = <<80/1=80>>80

After 81 weeks the chickens will be cheaper than buying eggs because 80 + 1 = <<80+1=81>>81

# Answer

81
<|im_start|>system
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<|im_start|>user
Roberto is raising chickens for eggs. He buys 4 chickens for $20 each. They cost $1 in total a week to feed and each produces 3 eggs a week that will last forever. He used to buy 1 dozen eggs a week and spent $2 per dozen. After how many weeks will the chickens be cheaper than buying his eggs?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
81
Roberto is raising chickens for eggs. He buys 4 chickens for $20 each. They cost $1 in total a week to feed and each produces 3 eggs a week that will last forever. He used to buy 1 dozen eggs a week and spent $2 per dozen. After how many weeks will the chickens be cheaper than buying his eggs?
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