The fuel consumption in miles per gallon for a car varies inversely with its weight. Suppose a car that weighs 3,000 pounds gets 28.7 miles per gallon on the highway. Write the equation that relates y, the fuel consumption in miles per gallon, to the car’s weight, w pounds. How many miles per gallon would a car get, if it weighs 4,100 pounds?

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Answer:

y = 86100 / w.

21 miles per gallon.

Step-by-step explanation:

If y is the consumption then:

y  = k / w   where k is some constant so we have:

28.7 = k / 3000

k = 3000 *28.7 = 86100

So the required equation is y = 86100 / w.

For a car weighing  4100 pounds:

y =  86100 / 4100 = 21 miles per gallon.

The required inverse relation is, yw = 86100.

The car will get 21 miles per gallon if it weighs 4,100 pounds.

What are direct and inverse relations?

A direct relation between two quantities implies that the increase in one increases the other and vice-versa.

If quantity a and b are directly related, then we write the relation as a ∝ b, which can be written as a = kb, where k is the constant of proportionality used to replace the proportionality symbol with the equal to sign.

An inverse relation between two quantities implies that the increase in one decreases the other and vice-versa.

If quantity a and b are inversely related, then we write the relation as a ∝ 1/b, which can be written as a = k/b, or, ab = k, where k is the constant of proportionality used to replace the proportionality symbol with the equal to sign.

How to solve the question?

In the question, we are given that the fuel consumption in miles per gallon (y) for a car inversely varies with its weight (w).

Thus we can write the relation like this:

y ∝ 1/w

or, y = k/w

or, yw = k.

The value of k can be determined using the given value of y = 28.7 miles per gallon and w = 3000 pounds.

Therefore, 28.7*3000 = k

or, k = 86100.

Thus, the required inverse relation is, yw = 86100.

Now, we are asked how many miles per gallon will a car get if it weighs 4100 pounds.

Therefore, w = 4100, y = ?

We know, yw = 86100.

or, y = 86100/w = 86100/4100 = 21.

Therefore, the car will get 21 miles per gallon, if it weighs 4,100 pounds.

Learn more about direct and inverse relations at

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