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What is the ratio of the number of people whose age is 18 or greater b [#permalink]
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Okay this is how I did it.
We have to find the ratio of number of people whose age is 18 or greater but less than 25, and number of people whose age is 25 or greater but less than 40.

Step 1
No. of people more than 18 but less than 25 (18<x<25)=

No of people 25 years and more - No. of people whose age is 18 years or greater

690 - 510 = 180

Step 2

No. of people whose age is 25 or more but less than 40:

No. of People less than 40 years old - No. of people less than 18 - number of people whose age is 18 or more but below 25 (calculated above)

810 - 420 - 180 = 210

Step 3

Ratio = 180:210 which is 6:7

Answer: A
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Re: What is the ratio of the number of people whose age is 18 or greater b [#permalink]
VERITAS Prep Solution:

Solution: The easiest way to solve this question may be to visually present the given information using a number line:

Attachment:
Screen Shot 2018-10-03 at 12.17.58 AM.png
Screen Shot 2018-10-03 at 12.17.58 AM.png [ 38.82 KiB | Viewed 8146 times ]


Since we know number of people who are less than 18 yrs old (420), and also those who are 18 yrs and more (690), we know the total population would be the sum of the two groups, i.e., 420 + 690 = 1110.

Using this, we can determine the number of people who are less than 25 yrs is 1110 – 510 = 600. So to find number of people who are between the ages of 18 and 25, we simply subtract the number of people below age 18. 600 – 420 = 180.

The number of people of age 40 yrs or more is 1110 – 810 = 300. We subtract this from the number of people age 25 years or more to find the group older than 25 and younger than 40, i.e., 510 – 300 = 210. The ratio between these two groups is 180:210, or 6:7. 
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Re: What is the ratio of the number of people whose age is 18 or greater b [#permalink]
Goal Ratio [18-25[ : [25-40[

People less than 18: 420

People less than 40 : 810


People between 40 and 18 is 810-420 =390

For any ratio, we have the relationship a (x) : b(x) : (a+b)x , example 1n:2n:3n

so we know that the sum of a and b need to be a factor of 390 (factors are 39 *10 , or 3*13*2*5)

only answer choice a) is a factor 6+7 = 13

b) = 40

c) = 40

d) =37

e) well A) already works..
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Re: What is the ratio of the number of people whose age is 18 or greater b [#permalink]
PathFinder007 wrote:
The following table gives some data collected about the population of a town by age:

What is the ratio of the number of people whose age is 18 or greater but less than 25 to the number of people whose age is 25 or greater but less than 40?

A. 6:7
B. 23:17
C. 17:23
D. 18:19
E. Cannot be determined

Attachment:
Karishma_Quant12.png


Total number of people = (less than 18 yrs) + (18 years or more) = 420 + 810 = 1,110

18 or greater but less than 25 = 690 - 510 - 180
25 or greater but less than 400 = (less than 40) - (less than 18) - 180 = 810 - 420 - 180 = 210

180 : 210
6: 7

Answer is A.
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What is the ratio of the number of people whose age is 18 or greater b [#permalink]
Bunuel VeritasKarishma ScottTargetTestPrep chetan2u

Total population = (Less than 18 yrs) + (18 yrs or more) = 420 + 690 = 1100

Finding numerator: The number of people whose age is 18 or greater but less than 25 = [18, 25)
Method#1: (18 yrs and more) - (25 yrs and more) = 690 - 510 = 180
Method#2: (Total population) - (Less than 18 yrs) - (more than 25 yrs) = 1100 - 420 - 510 = 170

Why don't they equal? Did I miss something?
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Re: What is the ratio of the number of people whose age is 18 or greater b [#permalink]
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TorGmatGod wrote:
Bunuel VeritasKarishma ScottTargetTestPrep chetan2u

Total population = (Less than 18 yrs) + (18 yrs or more) = 420 + 690 = 1100

Finding numerator: The number of people whose age is 18 or greater but less than 25 = [18, 25)
Method#1: (18 yrs and more) - (25 yrs and more) = 690 - 510 = 180
Method#2: (Total population) - (Less than 18 yrs) - (more than 25 yrs) = 1100 - 420 - 510 = 170

Why don't they equal? Did I miss something?



Total population is 420+690 or 1110.
So answer is 1110-420-510=180
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