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how many pounds of 60-40 solder (60% tin, 40% lead) must be mixed with 40-60 solder to produce 60 grams of 55-45 solder?
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Let x be "how many pounds of 60-40 solder (60% tin, 40% lead) must be mixed".
Then the governing equation is
0.6x + 0.4(60-x) = 0.55*60, or
0.6x + 24 - 0.4x = 33, or
0.2x = 33 - 24,
0.2x = 9,
x = = 45.
Answer. Mix 45 gram of 60-40 solder with 60-45 = 15 gram of 40-60 solder.
Check by tin. 0.6*45 + 0.4*15 = 33. 0.55*30 = 33. Correct!
Check by lead. 0.4*45 + 0.6*15 = 27. 0.55*60 = 27. Correct!
