SOLUTION: I am stuck on this question. The formula f(x)=2x^2+22x+320 models the number of inmates(in thousands) in US State and federal prisons x years after 1980. A) In which year were th

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Question 383508: I am stuck on this question. The formula f(x)=2x^2+22x+320 models the number of inmates(in thousands) in US State and federal prisons x years after 1980.
A) In which year were there 740 thousand inmates in US state and federal prisons? I started with adding 740 to the 320 and then broke it down and if I am right i got 2(x^2+11+530). But not sure where to go from here.
B) In which year where there 1100 thousand inmates in US state and federal prisons?
This is in review for my finals. Any help is great
Thank you
Found 2 solutions by richard1234, Edwin McCravy:
Answer by richard1234(7193)   (Show Source): You can put this solution on YOUR website!
For both parts you need to plug in 740 and 1,100 into f(x) to obtain an equation such as

which can be solved by the quadratic formula.
Answer by Edwin McCravy(20060)   (Show Source): You can put this solution on YOUR website!
I am stuck on this question. The formula models the number of inmates(in thousands) in US State and federal prisons x years after 1980.
A) In which year were there 740 thousand inmates in US state and federal prisons?
x = the number of years after 1980.

f(x) = the number of thoiusands of inmates in the year which is x years after 1980

A) In which year were there 740 thousand inmates in US state and federal prisons?
x = the number of years after 1980 = ?  (That's what we want to find)

f(x) = the number of inmates in the year which is x years after 1980 = 740  (That is given)

So we substitute 740 for f(x) in 





Can you solve that? If not post again asking how.

Solutions are x = 10 and x = -21

We ignore the negative value and our final answer is

10 years after 1980, or the year 1990.

B) In which year where there 1100 thousand inmates in US state and federal prisons?

x = the number of years after 1980 = ? (That's what we want to find)

f(x) = the number of inmates in the year which is x years after 1980 = 1100  (That is given)

So we substitute 1100 for f(x) in 





Can you solve that? If not post again asking how.

Solutions are x = 15 and x = -26

We ignore the negative value and our final answer is

15 years after 1980, or the year 1995.

Edwin
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