Pre Calc hw question?

Question

Let y= P(t) give the population of a town (in thous) t years after 1989. Suppose that P is a linear function and that the population was 18,000 in 1985 and 21,000 in 1989...

Question:

Find a formula for P(t)

if u could help me that would be great thank you!!!!!

Just to let everyone know. i have tried these problems like 10 times and still dont get it. so im not taking the easy way out. none of my peers or online or available to help me, so i thought the nice people of yahoo answers could. thanks.

infiniti i tried that... can the answer be a really large number????

Answer 1

Answer #2 is wrong...you have the wrong sign on the b value.

easy...This is grade 9 basic math.

The first thing is you find the slope.

The slope is the difference in y/difference in x

So you would take 21000-18000/1989-1985

that would give you a slope of 750.

We will treat the year 1985 as year zero. This will make the problem easier.

so now you plug in one of the points (0,18000) into the base equation y=m(x)+b

m=slope which we found out to be 750

so 18000=m(0) +b

so b is equal to 18000

therfore p(t)=750t+18000

if you didsn't use year 1985 as 0 your answer Should be p(t)=750x- 1470750

remember that the year is not plugged in as the actual year but the difference between it and the 1985 year. So 1990 would be year 5. The year 1 would be subbed in as -1984.

Wasn't that easy

If you want more help...Email me :)

BTW..it may not be the same as the one in your book. There is more than one possible way to write these types of problems. I'm not sure if your book consideres the year 1985 year 0, but my answer is still right. Try it..for the year 1989 and you will see it right.

Answer 2

lol this is precalc? It looks more like algebra to me. Well, what you do is you find the slope of the two points using y2-y1/x2-x1, then you
plug that into the equation y=mx+b and find the intercept

you should get 750 for the slope
y=750x + b

plug in one of the points into the equation

18000=750(1985) + b
so b= 1470750

therefore the equation should be y=750x + 1470750

Answer 3

P sub t = P * (1 + r)^t

where P is the starting population
r is the growth/decay rate - in years
t is time in years


your date needs to be a little more specific...I'm going to assume that the pop. was 18000 at the end of '85 and the pop was 21000 at the end of '89.....that gives a difference of 4 years...if you meant that the pop was 18000 at the start of '85...that would give you 5 years...

note....the "time" of r and t must match

21000 = 18000 (1 + r) ^ 4

21/18 = (1 + r) ^4

log (21/18) = 4 * log ( 1 + r)


the rest ....you can finish

Answer 4

Does your maths teacher know you be doing the easy way to do your homework?