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ruplun: Master | Next Rank: 500 Posts; Posts: 232; Joined: Fri Jun 18, 2010 7:09 am; Thanked: 1 times; Followed by:2 members

population

by ruplun » Wed Mar 07, 2012 10:16 am

The population of Linterhast was 3,600 people in 1990 and 4,800 people in 1993. If the population growth rate per thousand is constant, then what will be the population in 1996?

(A) 6,000
(B) 6,400
(C) 7,200
(D) 8,000
(E) 9,600

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Source: Beat The GMAT — Problem Solving | Wed Mar 07, 2012 10:16 am

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pm; Location: Vancouver, BC; Thanked: 5254 times; Followed by:1268 members; GMAT Score:770

by Brent@GMATPrepNow » Wed Mar 07, 2012 5:11 pm

ruplun wrote:The population of Linterhast was 3,600 people in 1990 and 4,800 people in 1993. If the population growth rate per thousand is constant, then what will be the population in 1996?

(A) 6,000
(B) 6,400
(C) 7,200
(D) 8,000
(E) 9,600

To calculate the growth rate, we'll use the formula: (new value - old value)/(old value)

Fortunately, the question tells us the increase over a 3-year period and asks for the population in another 3 years. So, all we need to do is calculate the 3-year growth rate.

The 3-year growth rate from 1990 to 1993 = (4800-3600)/3600 = 1200/3600 = 1/3

So, every three years, the population increases by 1/3

So, in the next 3 years, the population increase will be 1/3 of 4800 (which is 1600)

This means that the 1996 population will be [spoiler]4800+1600 = 6400 = B[/spoiler]

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com