Math Problem Statement

The annual profits for a company are given in the following table, where x represents the number of years since 1995, and y represents the profit in thousands of dollars. Write the linear regression equation that represents this set of data, rounding all coefficients to the nearest hundredth. Using this equation, estimate the calendar year in which the profits would reach 244 thousand dollars. Years since 1995 (x) Profits (y) (in thousands of dollars) 0 96 1 122 2 147 3 147

Solution

To determine the linear regression equation, we first need to find the equation in the form:

y=mx+by = mx + b

where:

  • mm is the slope.
  • bb is the y-intercept.

The data points given are:

  • (x1,y1)=(0,96)(x_1, y_1) = (0, 96)
  • (x2,y2)=(1,122)(x_2, y_2) = (1, 122)
  • (x3,y3)=(2,147)(x_3, y_3) = (2, 147)
  • (x4,y4)=(3,147)(x_4, y_4) = (3, 147)

Step 1: Calculate the Slope (mm)

The slope mm is given by:

m=nxy(x)(y)nx2(x)2m = \frac{n\sum{xy} - (\sum{x})(\sum{y})}{n\sum{x^2} - (\sum{x})^2}

Where:

  • nn is the number of data points.
  • xy\sum{xy} is the sum of the products of each xx and corresponding yy.
  • x\sum{x} is the sum of all xx values.
  • y\sum{y} is the sum of all yy values.
  • x2\sum{x^2} is the sum of the squares of all xx values.

Step 2: Calculate the Intercept (bb)

The intercept bb is given by:

b=ymxnb = \frac{\sum{y} - m\sum{x}}{n}

Calculations:

First, let's compute the sums:

  • x=0+1+2+3=6\sum{x} = 0 + 1 + 2 + 3 = 6
  • y=96+122+147+147=512\sum{y} = 96 + 122 + 147 + 147 = 512
  • xy=(0)(96)+(1)(122)+(2)(147)+(3)(147)=0+122+294+441=857\sum{xy} = (0)(96) + (1)(122) + (2)(147) + (3)(147) = 0 + 122 + 294 + 441 = 857
  • x2=02+12+22+32=0+1+4+9=14\sum{x^2} = 0^2 + 1^2 + 2^2 + 3^2 = 0 + 1 + 4 + 9 = 14

Now, using the slope formula:

m=4(857)(6)(512)4(14)(6)2=342830725636=35620=17.8m = \frac{4(857) - (6)(512)}{4(14) - (6)^2} = \frac{3428 - 3072}{56 - 36} = \frac{356}{20} = 17.8

Next, calculate the intercept bb:

b=51217.8×64=512106.84=405.24=101.3b = \frac{512 - 17.8 \times 6}{4} = \frac{512 - 106.8}{4} = \frac{405.2}{4} = 101.3

The Linear Regression Equation:

The linear regression equation is:

y=17.8x+101.3y = 17.8x + 101.3

Step 3: Estimate the Year in Which Profits Reach 244 Thousand Dollars

Set y=244y = 244 and solve for xx:

244=17.8x+101.3244 = 17.8x + 101.3

17.8x=244101.317.8x = 244 - 101.3

17.8x=142.717.8x = 142.7

x=142.717.88.02x = \frac{142.7}{17.8} \approx 8.02

So, the company is estimated to reach a profit of 244 thousand dollars approximately 8 years after 1995, which corresponds to the calendar year 2003.

Would you like more details on any part of the solution or have any questions? Here are some related problems:

  1. How would the equation change if the profits were in millions instead of thousands?
  2. What would the equation be if the profits had grown at a constant percentage instead of linearly?
  3. How would the estimate change if the data points included an outlier?
  4. Can the data be modeled more accurately with a quadratic equation?
  5. How would the equation be affected if you started tracking the years from 2000 instead of 1995?

Tip: Linear regression assumes a straight-line relationship. If the actual trend isn’t linear, a different model might be more appropriate.

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Math Problem Analysis

Mathematical Concepts

Linear Regression
Slope
Y-intercept

Formulas

Slope formula
Y-intercept formula

Theorems

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Suitable Grade Level

Grades 9-12