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There is some water in a bowl, which is on a electronic scales. Mike pours water into the bowl. After pouring $2$ glasses of water, the sacle shows $300$ grams. After pouring a total of $6$ glasses of water, the scale shows $700$ grams. What is the quality of the water at the start? 
Overseas Competition->Knowledge Point->Calculation Modules
The quality of each glass of water: $(700 - 300) \div (6 - 2) = 100$ g  At first: $300 - 100 \times 2 = 100$ g 