Hi Jen;

I assume "4700 people" is 4700 people/year.

**I also assume this is a ten year period of 1990-2000, not 100 years from 1900-2000. Please correct me if I am wrong.**

S=initial population of Seattle

S+[(4,700 people/year)(10 years)]=565,000 people

Let's solve...

Let's note the fact that the unit of year is in both the denominator and numerator. It cancels...

S+[(4,700 people/year)(10
years)]=565,000 people

S+[(4,700 people)(10)]=565,000 people

The only unit remaining is people. This is what we want.

S+47,000 people=565,000 people

Let's subtract 47,000 from both sides...

S+47,000-47,000=565,000-47,000

S=518,000

B=initial population of Baltimore

B-[(8,400 people/year)(10 years)=650,000 people

B-[(8,400 people/year)(10
years)=650,000 people

B-[(8,400 people)(10)]=650,000 people

B-84,000 people=650,000 people

B-84,000 people+84,000 people=650,000 people + 84,000 people

B=734,000

x=quantity of years for both populations to be equal...

(518,000 people)+[(4,700 people/year)(x years)]=(734,000 people)-[(8,400 people/year)(x years)]

The unit of years is in the numerator and denominator of the bracketed equations. It cancels...

(518,000 people)+[(4,700 people/year)(x
years)]=(734,000 people)-[(8,400 people/year)(x
years)]

(518,000 people)+[(4,700 people)(x)]=(734,000 people)-[(8,400 people)(x)]

The unit of people is in the numerator of all facets of the equation. It cancels...

(518,000 people)+[(4,700
people)(x)]=(734,000 people)-[(8,400
people)(x)]

(518,000)+[4,700(x)]=(734,000)-[8,400(x)]

Let's subtract 518,000 from both sides...

4,700(x)=216,000-[8,400(x)]

Let's add 8,400(x) to both sides...

13,100x=216,000

Let's divide both sides by 13,100...

x=16 years

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