Question
Paul has some black and grey balls. The total mass of all his balls is 197 g. He has 9 more grey balls than black balls. The average mass of the black balls is 7 g. The average mass of the grey balls is 13 g. How many balls does Paul have altogether?
3 m

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Paul has some black and grey balls. The total mass of all his balls is 197 g. He has 9 more grey balls than black balls. The average mass of the black balls is 7 g. The average mass of the grey balls is 13 g. How many balls does Paul have altogether?