Last visit was: 17 May 2024, 20:17 It is currently 17 May 2024, 20:17
Toolkit
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
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

The youngest of 4 children has siblings who are 3, 5, and 8 years olde

SORT BY:
Tags:
Show Tags
Hide Tags
Math Expert
Joined: 02 Sep 2009
Posts: 93334
Own Kudos [?]: 624550 [3]
Given Kudos: 81898
GMAT Club Legend
Joined: 12 Sep 2015
Posts: 6817
Own Kudos [?]: 30243 [3]
Given Kudos: 799
General Discussion
Board of Directors
Joined: 11 Jun 2011
Status:QA & VA Forum Moderator
Posts: 6069
Own Kudos [?]: 4704 [0]
Given Kudos: 463
Location: India
GPA: 3.5
Director
Joined: 20 Feb 2015
Posts: 630
Own Kudos [?]: 718 [0]
Given Kudos: 74
Concentration: Strategy, General Management
Re: The youngest of 4 children has siblings who are 3, 5, and 8 years olde [#permalink]
let the youngest be Y
sum of ages of all the children = 4y+16=4*(avg)
4y+16=84
y=17
GMAT Club Legend
Joined: 19 Dec 2014
Status:GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Posts: 21843
Own Kudos [?]: 11684 [0]
Given Kudos: 450
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: The youngest of 4 children has siblings who are 3, 5, and 8 years olde [#permalink]
Hi All,

This question can be solved by TESTing THE ANSWERS.

We're told that the YOUNGEST of 4 children has siblings who are 3, 5, and 8 years OLDER than she is and that the average age of the 4 siblings is 21. We're asked for the age of the youngest sibling.

Since the average age is 21 and we're trying to figure out the age of the YOUNGEST sibling, we should look for an answer that is several years LESS than 21...

Let's TEST Answer B: 18 years

IF...
Youngest = 18
Siblings = 21, 23 and 26
Sum = 88
Average = 88/4 = 22
This is TOO HIGH (the average is supposed to be 21).

Since the average is too high, all 4 of the children are TOO OLD. There's only one answer left that would lower the average...

GMAT assassins aren't born, they're made,
Rich
Manager
Joined: 02 Jun 2015
Posts: 61
Own Kudos [?]: 61 [0]
Given Kudos: 14
Location: Brazil
Concentration: Entrepreneurship, General Management
GPA: 3.3
Re: The youngest of 4 children has siblings who are 3, 5, and 8 years olde [#permalink]
Testing the answer in my opinion takes a long time.

We know that each one is 3,5,8 years OLDER

X + (3+X) + (5+X) + (8+X) = 21*4
4X + 16 = 84
4X = 68
X = 17
GMAT Club Legend
Joined: 19 Dec 2014
Status:GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Posts: 21843
Own Kudos [?]: 11684 [0]
Given Kudos: 450
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: The youngest of 4 children has siblings who are 3, 5, and 8 years olde [#permalink]
Hi douglasvg,

If you're not using Tactics (such as TEST THE ANSWERS) very often, then it might take you a little longer to use that approach right now (since you're not used to thinking in that way). However, in the long run - and on harder questions - those same Tactics can be extremely valuable.

1) How have you been scoring on your practice CATs (including the Quant and Verbal Scaled Scores)?
2) How is your pacing in the Quant section? Do you have to rush just to finish?

GMAT assassins aren't born, they're made,
Rich
Manager
Joined: 02 Jun 2015
Posts: 61
Own Kudos [?]: 61 [0]
Given Kudos: 14
Location: Brazil
Concentration: Entrepreneurship, General Management
GPA: 3.3
Re: The youngest of 4 children has siblings who are 3, 5, and 8 years olde [#permalink]
EMPOWERgmatRichC wrote:
Hi douglasvg,

If you're not using Tactics (such as TEST THE ANSWERS) very often, then it might take you a little longer to use that approach right now (since you're not used to thinking in that way). However, in the long run - and on harder questions - those same Tactics can be extremely valuable.

1) How have you been scoring on your practice CATs (including the Quant and Verbal Scaled Scores)?
2) How is your pacing in the Quant section? Do you have to rush just to finish?

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

On GMATPREP software Im scoring between 45-50 in quant
For hard question I indeed use it, then its a fast way to solve it.

Thank you Empower
Intern
Joined: 15 Aug 2017
Posts: 7
Own Kudos [?]: 7 [1]
Given Kudos: 33
Re: The youngest of 4 children has siblings who are 3, 5, and 8 years olde [#permalink]
1
Kudos
X + (3+X) + (5+X) + (8+X) = 21*4
4 X + 16 = 84
4 X = 68
X = 17
Target Test Prep Representative
Joined: 04 Mar 2011
Affiliations: Target Test Prep
Posts: 3042
Own Kudos [?]: 6353 [0]
Given Kudos: 1646
Re: The youngest of 4 children has siblings who are 3, 5, and 8 years olde [#permalink]
Bunuel wrote:
The youngest of 4 children has siblings who are 3, 5, and 8 years older than she is. If the average (arithmetic mean) age of the 4 siblings is 21, what is the age of the youngest sibling?

A. 17
B. 18
C. 19
D. 21
E. 22

We can let x = the age of the youngest child; thus, the ages of the three older children are x + 3, x + 5 and x + 8, respectively. We can create the equation:

(x + x + 3 + x + 5 + x + 8)/4 = 21

4x + 16 = 84

4x = 68

x = 17

Intern
Joined: 29 Sep 2018
Posts: 8
Own Kudos [?]: 3 [0]
Given Kudos: 1
Re: The youngest of 4 children has siblings who are 3, 5, and 8 years olde [#permalink]
If the average age of the 4 siblings is 21, we can determine the sum of ages by reversing division by 4.

$$\frac{x}{4}= 21$$
$$x = 4*21$$
$$x = 84$$

From there, we can set up an equation to find the age of the youngest child based on their age relative to their siblings.

If the youngest child = x:

$$x + (x+3) + (x+5) + (x+8) = 84$$
$$4x + 16 = 84$$
$$4x = 68$$
$$x = 17$$

Therefore, the youngest child is 17 (option A).
Non-Human User
Joined: 09 Sep 2013
Posts: 33058
Own Kudos [?]: 828 [0]
Given Kudos: 0
Re: The youngest of 4 children has siblings who are 3, 5, and 8 years olde [#permalink]
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
Re: The youngest of 4 children has siblings who are 3, 5, and 8 years olde [#permalink]
Moderators:
Math Expert
93334 posts
Senior Moderator - Masters Forum
3137 posts