Question

Phil is riding his bike. He rides 25 miles in 2 hours, 37.5 miles in 3 hours, and 50
miles in 4 hours. Find the constant of proportipnality and write an equation to
describe the situation. Let x represent the number of hours.
The equation that describes the relationship is y =

Answer 1

The constant of proportionality (known as "speed" in this case) is 12.5 miles per hour.

The equation is  

d

=

12.5

×

t

Explanation:

To find the constant of proportionality, divide one value in each pair by the other. If this relationship is a true direct proportionality , when you repeat these for every pair, your will come up with the same value:

For example

25

miles

÷

2

hours

=

12.5

miles

hour

A direct proportionality will always result in an equation that resembles this:

y

=

k

x

where  

y

and  

x

are the related quantities and  

k

is the constant of proportionality. If you draw a graph using the values you have, the graph will show a straight line the passes through the origin. The slope of this line will be the constant of proportionality. (And if the values given are real physical quantities, this constant will contain important information about the situation you are studying!)