"the first type costs $2 per pound and the second costs $7 per pound. how much of each type does mavis use to make 50 pounds of a blend which costs $5 per pound?

   First type (x) = 20 pounds

Second type(y) = 30 pounds

Step-by-step explanation:

Consider,

First type as x and second type as y.

Making linear equations:

   x + y = 501)

2x + 7y = (5*50)

2x + 7y = 2502)

Solving above two simultaneous equations:

From first equation: y = 50-x

put this into second equation:

2x + 7(50-x) = 250

Solving for x:

2x + 350 -7x = 250

               -5x = -100

                   x = 20

Putting x = 20 in first equation:

            20 +y = 50

                    y = 50-20 = 30

Therefore,

x = 20

y = 30

First type (x) = 20 pounds

Second type (y) = 30 pounds

answer: the common difference is -0.10

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