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Peter Rabbit eats cabbages and carrots. Each day he eats either $$10$$ carrots or $$2$$ cabbages. Last week Peter ate $$6$$ cabbages. How many carrots did he eat last week? (2014 Math Kangaroo Problem, Level 1-2, Question \#18) 
Overseas Competition->Knowledge Point->Calculation Modules->Whole Numbers->Mixed Operations
Peter ate $6$ cabbages in $6\div2=3$ days. In $7-3=4$ days, Peter ate $4\times10=10+10+10+10=40$ carrots. 