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The population \( y \) (in millions) of two states in year \( x \) can be approximated by the following, where \( x=10 \) corresponds to the year 2010. In what year did the two states have the same population? What was the population of these states at that time? State A: \( \quad 10 y-x=84 \) State B: \( 100 y-x=975 \) The two states had the same population in the year \( \square \). The population of these states at that time was million. (Type integers or decimals.)

Ask by Graham Maxwell. in the United States
Mar 10,2025

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Tutor-Verified Answer

Answer

The two states had the same population in the year 2015, and the population at that time was 9.9 million.

Solution

We are given the equations: \[ 10y - x = 84 \quad \text{(State A)} \] \[ 100y - x = 975 \quad \text{(State B)} \] First, solve each equation for \( y \). For State A: \[ 10y = x + 84 \quad \Rightarrow \quad y = \frac{x + 84}{10} \] For State B: \[ 100y = x + 975 \quad \Rightarrow \quad y = \frac{x + 975}{100} \] Since the populations are equal at the same time, set the two expressions for \( y \) equal to each other: \[ \frac{x + 84}{10} = \frac{x + 975}{100} \] To eliminate the denominators, multiply both sides by 100: \[ 100\left(\frac{x + 84}{10}\right) = x + 975 \quad \Rightarrow \quad 10(x + 84) = x + 975 \] Simplify the equation: \[ 10x + 840 = x + 975 \] Subtract \( x \) from both sides: \[ 9x + 840 = 975 \] Subtract 840 from both sides: \[ 9x = 135 \] Solve for \( x \): \[ x = \frac{135}{9} = 15 \] Since \( x = 10 \) corresponds to the year 2010, \( x = 15 \) corresponds to: \[ 2010 + (15 - 10) = 2015 \] Now, substitute \( x = 15 \) back into one of the equations to find \( y \). Using State A: \[ y = \frac{15 + 84}{10} = \frac{99}{10} = 9.9 \] Thus, the two states had the same population in the year \( \boxed{2015} \) and the population at that time was \( \boxed{9.9 \text{ million}} \).

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The Deep Dive

To find the year when the populations of State A and State B were equal, we first need to rearrange the equations for each state and express the populations in terms of \( x \). For State A: \[ 10y - x = 84 \quad \text{(1)} \] Rearranging gives: \[ 10y = x + 84 \implies y = \frac{x + 84}{10} \quad \text{(2)} \] For State B: \[ 100y - x = 975 \quad \text{(3)} \] Rearranging gives: \[ 100y = x + 975 \implies y = \frac{x + 975}{100} \quad \text{(4)} \] Now, we set equations (2) and (4) equal to each other to find the year \( x \) when their populations are the same: \[ \frac{x + 84}{10} = \frac{x + 975}{100} \] To eliminate the fractions, multiply both sides by 1000: \[ 100(x + 84) = 10(x + 975) \] Expanding both sides: \[ 100x + 8400 = 10x + 9750 \] Rearranging gives: \[ 100x - 10x = 9750 - 8400 \] \[ 90x = 1350 \implies x = 15 \] Now, substituting \( x = 15 \) back into either equation (using State A's equation): \[ 10y - 15 = 84 \implies 10y = 99 \implies y = 9.9 \] Thus, the two states had the same population in the year \( 15 + 2000 = 2025 \). At that time, the population of these states was 9.9 million. The two states had the same population in the year \( 2025 \). The population of these states at that time was 9.9 million.

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