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From 1970 to 1990 the average per person annual consumption of whole milk declined at a constant rate from 101 to 41 quarts per year. During the same period, the average annual consumption of low fat milk increased at a constant rate from 25 to 60 quarts per year. What was the average annual per person consumption when the consumption of whole milk and low fat milk was the same?
Choose 1 answer:
(A) 53 quarts
(B) 55 quarts
(c) 57 quarts
(D) 59 quarts

From \(1970\) to \(1990\) the average per person annual consumption of whole milk declined at a constant rate from \(101\) to \(41\) quarts per year. During the same period, the average annual consumption of low fat milk increased at a constant rate from \(25\) to \(60\) quarts per year. What was the average annual per person consumption when the consumption of whole milk and low fat milk was the same?\newlineChoose 11 answer:\newline(A) \(53\) quarts\newline(B) \(55\) quarts\newline(C) \(57\) quarts\newline(D) \(59\) quarts

Full solution

Q. From \(1970\) to \(1990\) the average per person annual consumption of whole milk declined at a constant rate from \(101\) to \(41\) quarts per year. During the same period, the average annual consumption of low fat milk increased at a constant rate from \(25\) to \(60\) quarts per year. What was the average annual per person consumption when the consumption of whole milk and low fat milk was the same?\newlineChoose 11 answer:\newline(A) \(53\) quarts\newline(B) \(55\) quarts\newline(C) \(57\) quarts\newline(D) \(59\) quarts
  1. Determine rate of decline for whole milk: Determine the rate of decline for whole milk consumption.\newlineThe decline in whole milk consumption over 2020 years (from 19701970 to 19901990) is from 101101 quarts to 4141 quarts. This is a total decline of 10141=60101 - 41 = 60 quarts over 2020 years.\newlineRate of decline for whole milk=Total declineNumber of years=60 quarts20 years=3 quarts per year\text{Rate of decline for whole milk} = \frac{\text{Total decline}}{\text{Number of years}} = \frac{60 \text{ quarts}}{20 \text{ years}} = 3 \text{ quarts per year}
  2. Determine rate of increase for low fat milk: Determine the rate of increase for low fat milk consumption.\newlineThe increase in low fat milk consumption over the same 2020 years is from 2525 quarts to 6060 quarts. This is a total increase of 6025=3560 - 25 = 35 quarts over 2020 years.\newlineRate of increase for low fat milk=Total increaseNumber of years=35 quarts20 years=1.75quarts per year\text{Rate of increase for low fat milk} = \frac{\text{Total increase}}{\text{Number of years}} = \frac{35 \text{ quarts}}{20 \text{ years}} = 1.75 \text{quarts per year}
  3. Set up equation for equal milk consumption: Set up an equation to find the year when the consumption of whole milk and low fat milk was the same.\newlineLet xx be the number of years after 19701970 when the consumptions are equal.\newlineStarting with 101101 quarts for whole milk and subtracting 33 quarts per year, we get: 1013x101 - 3x.\newlineStarting with 2525 quarts for low fat milk and adding 1.751.75 quarts per year, we get: 25+1.75x25 + 1.75x.\newlineSet the two expressions equal to each other: 1013x=25+1.75x101 - 3x = 25 + 1.75x
  4. Solve equation for x: Solve the equation for x.\newlineCombine like terms: 10125=3x+1.75x101 - 25 = 3x + 1.75x\newline76=4.75x76 = 4.75x\newlineDivide both sides by 4.754.75 to solve for xx: x=764.75x = \frac{76}{4.75}\newlinex16x \approx 16
  5. Calculate average annual consumption: Calculate the average annual per person consumption when the consumptions are equal.\newlineSubstitute xx back into either the whole milk or low fat milk equation: 1013(16)101 - 3(16) or 25+1.75(16)25 + 1.75(16).\newlineUsing the whole milk equation: 1013(16)=10148=53101 - 3(16) = 101 - 48 = 53 quarts.\newlineUsing the low fat milk equation: 25+1.75(16)=25+28=5325 + 1.75(16) = 25 + 28 = 53 quarts.\newlineBoth equations should give the same result, which is the point where the consumptions are equal.

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