Question 182906
Your boss wants to know how much of the 87% material is needed to blend with the 5000 pounds of the 123% material so that the final strength of the blended material is 100% strength. What do you tell him? 
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Equation:
0.87x + 1.23(5000) = 1.00(5000+x)

Multiply thru by 100 to get:

87x + 123*5000 = 5000 + x
86x = -122*5000
x = -7093.023
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There is no positive solution to the problem.
There is no amount of 123% material that can be added 
to produce a 100% strenth mixture.
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Cheers,
Stan H.