Exercise 18 Page 335

We want to write an equation that represents the amount of water, y, that passes through the point in x minutes. Let's start by recalling that when two quantities x and y are proportional,

they are related by a constant of proportionality, k. Then, the relationship between the two quantities can be expressed with an equation.

y = kx We can use this information to write the equation. We can start by calculating the constant of proportionality. We know that 600 000 gallons of water pass through a given point along a river every minute. This means that we can substitute 600 000 gallons for y and 1 for x in our equation.

y=kx

SubstituteII

y= 600 000, x= 1

600 000=k( 1)

IdPropMult

Identity Property of Multiplication

600 000=k

RearrangeEqn

Rearrange equation

k=600 000

Now, we can substitute 600 000 for k in our proportional equation. y = kx ⇒ y=600 000x This result corresponds to answer B.