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John has 54 marbles. some are red and some are black. The ratio of the number red marbles to black are 7:2. How may more red than black are there?

Respuesta :

Red : Black : Total 
7 : 2 : 7+2 
7 : 2 : 9

9x = 54
1x = 54÷9 = 6
7x = 7x6 = 42
2x = 2x6 = 12

Red : Black
42 : 12

42 - 12 = 30 
There are 30 more red than black


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