Question

In 1960 the world record for the men's mile was 3.91 minutes. In 1980, the record time was 3.81 minutes. Write a linear model that represents the world record for the men's mile as a function of the number of years since 1960.

Answer 1

$x$ - number of years passed since 1960
$y$ - time in minutes

A line $y=mx+n$ passes through the points (0,3.91) and (20,3.81).

Find slope.
$m= \frac{3.81-3.91}{20-0}= \frac{-0.1}{20}=-0.005$

Find $y$-intercept. 
$y=mx+n \\3.91=-0.005 \times 0+n \\n=3.91$

The equation of line is
$y=-0.005+3.91$