Question
Billy has some silver and grey balls. The total mass of all his balls is 219 g. He has 9 less silver balls than grey balls. The average mass of the silver balls is 6 g. The average mass of the grey balls is 7 g. How many balls does Billy have altogether?
3 m

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Billy has some silver and grey balls. The total mass of all his balls is 219 g. He has 9 less silver balls than grey balls. The average mass of the silver balls is 6 g. The average mass of the grey balls is 7 g. How many balls does Billy have altogether?