Question

A small rural town has experienced a population decrease at a rate of 25 people every 5 years since 1970. If the population of the town in 1970 was 250, which of the following equations represents the town’s population as a function of time? (Assume 1970 is represented by x = 0, 1971 is represented by x = 1, and so on).
A. y = –5x + 250
B. y = –25x + 250
C. –5x + y = 250
D. –x – 25y = 250

Answer 1

Here y is the population and x is the year since 1970.
 
The "population decreases at the rate of 25 people every 5 years"

slope of a line = difference in y / difference in x (or rise / run) = -25 / 5

slope m = -5

when x = 0 (that is the year 1970), the population is 250.
x = 0 represents the y-intercept

Answer is C. -5x+y=250