Answer:
First, remember the relation:
Distance = Time*Speed.
And a relation of proportionality between X and Y is:
Y = k*X
where k is the constant of proportionality.
First, we know that he needs 30 minutes to walk 2 miles, then we have the relation:
2mi = 30min*speed
Speed = 2mi/30min = (1/15) mi/min.
Then we can represent the relation between d and t in two different ways:
d = (1/15)mi/min*t
where the constant is = (1/15)mi/min and this means that in one minute, he walks 1/15 of a mile.
The other way of writing this is obtained by dividing at both sides by (1/15)mi/min:
t = 15min/mi*d
Now the constant is 15min/mi, which means that when he walks on mile, 15 minutes of time passes by.
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