First, find the linear equation:
Let the x-axis represents the years and the y-axis represents the price.
1977 (y₁) = 0 Price in 1977 (x₁) = 175
2004 (y₂) = 2004 - 1977 = 27 Price in 2004 (x₂) = 15
The two points are:
(1997, price) = (0, 175)
(2004, price) = (27, 15)
y-y₁ = [tex] \frac{y _{2}-y _{1} }{x _{2}-x _{1} } [/tex] (x - x₁)
y - 175 = -160/27 (x - 0)
y = -160/27 (x) + 175
y = -5.93x + 175 (Linear Equation)
Note that the slope (-160/27 or -5.93) is negative because the price
of the calculator is decreasing.
To find the price of calculator in 1998:
x₃ = 1998 - 1977
x₃ = 21
Plug-in 21 to x₃:
y₃ = -5.92(x₃) + 175
y₃ = -5.92 (21) + 175
y₃ = -124.32 + 175
y₃ ≈ 50.68 or $51
ANSWER: The price of calculator in 1998 is $50.68 or $51.