Question
Andy has some black and grey balls. The total mass of all his balls is 220 g. He has 7 more grey balls than black balls. The average mass of the black balls is 5 g. The average mass of the grey balls is 12 g. How many balls does Andy have altogether?
3 m

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Andy has some black and grey balls. The total mass of all his balls is 220 g. He has 7 more grey balls than black balls. The average mass of the black balls is 5 g. The average mass of the grey balls is 12 g. How many balls does Andy have altogether?