Question

The following formula models the number of prison inmates, P, in thousands, who are in U.S. prisons x years after 1980.

P
=
2
x
2
+
22
x
+
322
P=2x2+22x+322


Find the first year after 1980 in which the population of U.S. prisons was approximately 574 thousand people.

Answer 1

1987

Explanation:

If we consider x years after 1980, when the number of prisoners, P, in thousands, is given by

P = 2x² + 22x + 322 ......... (1)

Now, If the population of U.S. prisoners was approximately 574 thousand people, then we have to find the year of this situation.

Now, from equation (1), we get

574 = 2x² + 22x + 322

⇒ 2x² + 22x - 252 = 0

⇒ x² + 11x - 126 = 0

⇒ x² + 18x - 7x - 126 = 0

⇒ (x + 18) ( x - 7) = 0

⇒ x = 7

As x can not be negative so we neglect the x = - 18 value.

So, in the year 1987, the number of U.S. prisoners became approximately 574 thousand people. (Answer)