Now, let's say, we add "x" lbs of the 60% gold alloy, so.. how much gold is in it? well, is just 60%, so (60/100) * x, or 0.6x.
likewise, if we use "y" lbs of the 40% alloy, how much gold is in it? well, 40% of y, or (40/100) * y, or 0.4y.
now, whatever "x" and "y" are, their sum must be 12.4 lbs.
we also know that the gold amount in each added up, must equal that of the 50% resulting alloy.
how much of the 40% alloy? well, y = 12.4 - x.
likewise, if we use "y" lbs of the 40% alloy, how much gold is in it? well, 40% of y, or (40/100) * y, or 0.4y.
now, whatever "x" and "y" are, their sum must be 12.4 lbs.
we also know that the gold amount in each added up, must equal that of the 50% resulting alloy.
how much of the 40% alloy? well, y = 12.4 - x.