The Royal Fruit Company produces two types of fruit drinks. The first type is 40% pure fruit juice, and the second type is 60% pure fruit juice. The company is attempting to produce a fruit drink that contains 55% pure fruit juice. How many pints of each of the two existing types of drink must be used to make 140 pints of a mixture that is 55% pure fruit juice?

1 answer

Let x be the number of pints of the first type of fruit drink.
The number of pints of the second type of fruit drink is 140 - x.
40% of x pints of the first type of fruit drink is 0.4*x pints of pure fruit juice.
60% of (140 - x) pints of the second type of fruit drink is 0.6 * (140 - x) = 84 - 0.6x pints of pure fruit juice, since the second type of fruit drink is 60% pure fruit juice.
The resulting mixture contains (0.4x + 84 - 0.6x) = 84 - 0.2x pints of pure fruit juice.
The resulting mixture must contain 55% pure fruit juice, which can be written as 0.55 * 140 = 77 pints of pure fruit juice.
Therefore, 84 - 0.2x = 77.
Subtracting 84 from both sides of the equation, we get -0.2x = -7.
Dividing both sides of the equation by -0.2, we get x = -7 / -0.2 which simplifies to x = 35.
Therefore, 35 pints of the first type of fruit drink must be used, and since the total amount is 140 pints, the remaining 140 - 35 = <<140-35=105>>105 pints must be of the second type of fruit drink should be used. Answer: \boxed{35}.