Math problems for elementary school students

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Explanation of the steps:

Cat ++ Mouse =8kg=8๐‘˜๐‘”

Dog ++ Mouse =11kg=11๐‘˜๐‘”

Dog ++ Cat =15kg=15๐‘˜๐‘”

โ‡’2(โ‡’2(Cat ++ Mouse ++ Dog)=8+11+15=34)=8+11+15=34

โ‡’โ‡’ Cat ++ Mouse ++ Dog =34:2=17(kg).