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4 years ago

2.) The equation yˆ=−8.74x2+50.57x+39.02 models the number of customers in a store x hours after opening.

Mathematics

1 answer:

Artemon [7]4 years ago

7 0

Answer:

2. The correct option is;

D. 112

3. The predicted number of cellular subscription per 100 people in Australia in 2030 is 217 subscriptions

4. The equation of the quadratic regression curve is y = x² - 6×x + 4.1

5. The closest option is;

C. 4191

Step-by-step explanation:

2. The equation for the number of customers in a store is presented as follows;

y = -8.74·x² + 50.57·x + 39.02

Where:

x = Number of hours after opening

∴ When x = 3 hours

y = -8.74×3² + 50.57×3 + 39.02 = 112.07 ≈ 112 people

The correct option is D. 112

3. The expression of the regression equation is presented as follows

y = -0.107·x² + 9.008·x +28.851

Where:

x = Number of years since 1990, hence

When x = 2030 - 1990 = 40 Years

Hence, the predicted number of cellular subscriptions per people in 2030 is presented as follows;

y = -0.107×40² + 9.008×40 +28.851 = 217.971 Subscribers

To round down to the nearest whole number as y = 217 subscribers

4. The general form of a quadratic equation is presented as follows;

y = a·x² + b·x + c

When x = 0, y = 4.1, therefore;

4.1 = a×0² + b×0 + c = c

∴ c = 4.1

When x = 1, y = -0.9, therefore;

-0.9 = a×(1)² + b×1 + c = c

-0.9 = a + b + 4.1

∴ a + b = -0.9 - 4.1 = -5.0

When x = 2, y = -3.9, therefore;

-3.9 = a×(2)² + b×2 + c = c

-3.9 = 4·a + 2·b + 4.1

∴ 4·a + 2·b = -3.9 - 4.1 = -8.0

Thus we have two equations;

a + b = -5.0..................(1) and

4·a + 2·b = -8.0 ..........(2)

Multiply equation (1) by 2 and subtract it from equation (2), we have

4·a + 2·b - 2×(a + b) = *8.0 - (2 ×-5.0)

∴ 2·a = 2

a = 1

From equation (1,) we have;

a + b = -5.0..................(1)

Therefore, where a = 1 we have, 1 + b = -5.0

Hence, b = -5.0 - 1 = -6.0

Therefore, the equation of the quadratic regression curve is presented as follows;

y = x² - 6×x + 4.1

5. The quadratic regression equation is found as follows;

The general form of a quadratic equation is presented as follows;

y = a·x² + b·x + c

When x = 55, y = 3650, therefore;

3650= a×55² + b×55+ c................(1)

When x = 65, y = 4569, therefore;

4569= a×65² + b×65+ c ...........(2)

When x = 75, y = 6147, therefore;

6147= a×75² + b×75+ c............(3)

Solving the system of equation;

3650= a×55² + b×55+ c................(1)

4569= a×65² + b×65+ c ...........(2)

6147= a×75² + b×75+ c............(3)

Subtracting equation (1) from (2), we obtain;

4569 - 3650 = a×65² + b×65 + c - (a×55² + b×55 + c)

919 = 1200·a + 10·b...........(4)

Subtracting equation (2) from (3), we obtain;

6147 - 4569 = a×75² + b×75 + c - (a×65² + b×65+ c)

Which gives;

1578 = 1400·a + 10·b...........(5)

Subtracting equation (4) from equation (3), we obtain;

1578 - 919 = 1400·a + 10·b - (1200·a + 10·b)

659 = 200·a

a = 659/200= 3.295

Substituting the value of a in equation (4), we have;

919 = 1200×3.295 + 10·b = 3954 + 10·b

∴ 10·b = 919 -3954 = -3035

b = -3035/10 = -303.5

Substituting the value of a and b in equation (1), we have;

3650 = (3.295)×55² + (-303.5)×55+ c

3650 = -6725.125 + c

∴ c = 3650 - (- 6725.125)= 10375.125

Therefore, the quadratic regression equation is presented as follows;

y = 3.295·x - 303.5·b +10375.125

Hence, in 1961, x = 1961 - 1900 = 61, we have

y = 3.295×61² - 303.5×61 10375.125= 4122.32

Therefore, the closest option is C. 4191.

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