Amerchant has coffee worth $20 a pound that she wishes to mix with 30 pounds of coffee with $60 a pound to get a mixture that is worth $30 a pound. how many pounds of the $20 coffee should be used?

  90 pounds

Step-by-step explanation:

Let x represent the number of pounds of $20 coffee in the mix. Then the cost of the mix is ...

  20x + 60·30 = 30(30+x)

  20x + 1800 = 900 +30x . . . . . eliminate parentheses

  900 = 10x . . . . . . . . . . . . . . . . . subtract 900+20x

  90 = x . . . . . . . . . . . . . . . . . . . . divide by 10

90 pounds of $20 coffee should be used.

relating to or denoting a system of numbers and arithmetic based on the number ten, tenth parts, and powers of ten.

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