2009 AIME II Problems/Problem 1
Before starting to paint, Bill had ounces of blue paint, ounces of red paint, and ounces of white paint. Bill painted four equally sized stripes on a wall, making a blue stripe, a red stripe, a white stripe, and a pink stripe. Pink is a mixture of red and white, not necessarily in equal amounts. When Bill finished, he had equal amounts of blue, red, and white paint left. Find the total number of ounces of paint Bill had left.
After the pink stripe is drawn, all three colors will be used equally so the pink stripe must bring the amount of red and white paint down to ounces each. Say is the fraction of the pink paint that is red paint and is the size of each stripe. Then equations can be written: and . The second equation becomes and substituting the first equation into this one we get so . The amount of each color left over at the end is thus and .
We know that all the stripes are of equal size. We can then say that is the amount of pain per stripe. Then will be the amount of blue paint left. Now for the other two stripes. The amount of white paint left after the white stripe and the amount of red paint left after the blue stripe are and respectively. The pink stripe is also r ounces of paint, but let there be ounces of red paint in the mixture and ounces of white paint. We now have two equations: and . Solving yields k = 34 and r = 92. We now see that there will be ounces of paint left in each can.
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