GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 15 Oct 2019, 01:52

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# In the period between 1975 and 1985, the population of each of the …ve

Author Message
TAGS:

### Hide Tags

Senior Manager
Status: Manager
Joined: 02 Nov 2018
Posts: 280
In the period between 1975 and 1985, the population of each of the …ve  [#permalink]

### Show Tags

14 Apr 2019, 14:12
00:00

Difficulty:

45% (medium)

Question Stats:

53% (01:06) correct 47% (01:22) wrong based on 30 sessions

### HideShow timer Statistics

In the period between 1975 and 1985, the population of each of the five major cities in country C increased by at least 10,000 people. If the standard deviation of the populations in 1975 was 35,000 people, what was the standard deviation of the populations in 1985?

(1) The total increase in population of the five cities from 1975 to 1985 was 220,000 people.

(2) Each of the five cities increased in population by 12% in the period between 1975 and 1985.

_________________
Give a kudos if u find my post helpful. kudos motivates active discussions

Math Expert
Joined: 02 Aug 2009
Posts: 7958
Re: In the period between 1975 and 1985, the population of each of the …ve  [#permalink]

### Show Tags

14 Apr 2019, 19:31
In the period between 1975 and 1985, the population of each of the five major cities in country C increased by at least 10,000 people. If the standard deviation of the populations in 1975 was 35,000 people, what was the standard deviation of the populations in 1985?

(1) The total increase in population of the five cities from 1975 to 1985 was 220,000 people.

(2) Each of the five cities increased in population by 12% in the period between 1975 and 1985.

Some points on SD..
1. If you add or subtract same number from all elements, the SD remains the same as the spread of numbers remains the same. It is just that the set moves up or down in similar fashion
2. If you multiply each element by same number say x, multiply the SD by |x|

Ok.. we are given SD in 1975 and we are looking for SD in 1985.
Statement I tells us that the total increase is 220,000 during this period. But we require each element to get SD
Statement II tells us that each element increased by 12%, so each element is 1.12(element).. Hence SD will be 1.12(old SD)=1.12(35,000)
Sufficient

B
_________________
Re: In the period between 1975 and 1985, the population of each of the …ve   [#permalink] 14 Apr 2019, 19:31
Display posts from previous: Sort by