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4000 towels are for sale.the ratio of blue to red was 2:1.the rest were white. After 1/4 of the blue towels and
half of the white were sold, there were 2400 towels left. How many red and white towels were at first.
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Let x be the number of red towels initially.
Then the number of blue towels initially is 2x, according to the condition.
Let w be the number of white towels initially.
Then you have these two equations in 2 unknowns:
2x + x + w = 4000 (1) ("4000 towels are for sale.the ratio of blue to red was 2:1.the rest were white.")
= 2400 (2) ("After 1/4 of the blue towels and half of the white were sold, there were 2400 towels left")
Simplify. It includes multiplying eq(2) by 2 (both sides).
3x + w = 4000 (1')
3x + 2x + w = 4800 (2')
or
3x + w = 4000 (1'')
5x + w = 4800 (2'')
Now subtract eq(1'') from eq(2''). You will get
2x = 4800-4000 = 800 ====> x = = 400.
Answer. 400 red towels; 2*400 = 800 blue towels and 4000 - 400 - 800 = 2800 white towels.