The population of City A for each of three years...

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BTGmoderatorLU: Moderator; Posts: 2505; Joined: Sun Oct 15, 2017 1:50 pm; Followed by:6 members

The population of City A for each of three years...

by BTGmoderatorLU » Sun Jan 14, 2018 7:03 am

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The population of City A for each of three years is shown in the table above. If the population grew by m percent from 1970 to 1980 and n percent from 1980 to 1990, then m exceeds n by how much?

A. 37.5
B. 20
C. 17.5
D. 15
E. 12.5

The OA is C.

I'm confused with this PS question. Experts, any suggestion? I need to determine the value of n and m from the table but I'm not sure how can I do it. Thanks in advance.

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Source: Beat The GMAT — Problem Solving | Sun Jan 14, 2018 7:03 am

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by [email protected] » Sun Jan 14, 2018 11:03 am

Hi LUANDATO,

We're told that the population grew by M percent from 1970 to 1980 (40,000 to 55,000) and N percent from 1980 to 1990 (55,000 to 66,000). We're asked for how much M exceeds N. This question is essentially about using the Percentage Change Formula.

Percent Change = (New - Old)/Old

From 1970 to 1980.... (55,000 - 40,000)/(40,000) = 15,000/40,000 = 15/40 = 37.5/100
M = 37.5

From 1980 to 1990.... (66,000 - 55,000)/(55,000) = 11,000/55,000 = 1/5 = 20/100
N = 20

M exceeds N = 37.5 - 20 = 17.5

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Mon Aug 05, 2019 4:12 pm

BTGmoderatorLU wrote:

zoom here, https://postimg.cc/image/cbexbhn91/

The population of City A for each of three years is shown in the table above. If the population grew by m percent from 1970 to 1980 and n percent from 1980 to 1990, then m exceeds n by how much?

A. 37.5
B. 20
C. 17.5
D. 15
E. 12.5

The OA is C.

The percent increase from 1970 to 1980 is:

(55,000 - 40,000)/40,000 x 100

15,000/40,000 x 100

15/40 x 100

37.5

So m = 37.5 percent

Likewise, the percent increase from 1980 to 1990 is:

(66,000 - 55,000)/55,000 x 100

11,000/55,000 x 100

11/55 x 100

20

So n = 20 percent.

Therefore, m - n = 17.5 percent.

Answer: C

Scott Woodbury-Stewart
Founder and CEO
[email protected]