A Trussian's weight, in keils, can be calculated by taking the square root of his age in years. A Trussianteenager now weighs three keils less than he will seventeen years after he is twice as old as he is now. How old is he now?
(A) 14 (B) 15 (C) 16 (D) 17 (E) 18
Source: A local-GMAT-prep-company's material
Target Test Prep is 20% off right now!
Use code FLASH20
Available with Beat the GMAT members only code
MORE DETAILS
How old is he now?
This topic has expert replies
-
neelgandham
- Community Manager
- Posts: 1060
- Joined: Fri May 13, 2011 6:46 am
- Location: Utrecht, The Netherlands
- Thanked: 318 times
- Followed by:52 members
Anil Gandham
Welcome to BEATtheGMAT | Photography | Getting Started | BTG Community rules | MBA Watch
Check out GMAT Prep Now's online course at https://www.gmatprepnow.com/
Welcome to BEATtheGMAT | Photography | Getting Started | BTG Community rules | MBA Watch
Check out GMAT Prep Now's online course at https://www.gmatprepnow.com/
-
shankar.ashwin
- Legendary Member
- Posts: 966
- Joined: Sat Jan 02, 2010 8:06 am
- Thanked: 230 times
- Followed by:21 members
Start with answer choices
Choice C:
If his current age = 16, weight = 4
17 + 2(16) = 49, weight = 7
Difference = 7-4 = 3 - Satisfies given condition. C IMO
Choice C:
If his current age = 16, weight = 4
17 + 2(16) = 49, weight = 7
Difference = 7-4 = 3 - Satisfies given condition. C IMO
GMAT/MBA Expert
-
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
Agesneelgandham wrote:A Trussian's weight, in keils, can be calculated by taking the square root of his age in years. A Trussianteenager now weighs three keils less than he will seventeen years after he is twice as old as he is now. How old is he now?
(A) 14 (B) 15 (C) 16 (D) 17 (E) 18
Source: A local-GMAT-prep-company's material
Let today's age = T
So, 17 years after he is twice as old as he is now = 2T + 17
Weights
Today's weight = root(T)
Future weight = root(2T + 17)
Big step
A Trussianteenager now weighs three keils less than he will seventeen years after he is twice as old as he is now.
This tells us that: root(T) + 3 = root(2T + 17)
Solve for T
Square both sides: T + 6root(T) + 9 = 2T + 17
Simplify: 6root(T) = T + 8
At this point, we can see that T must be a perfect square. So, we'll check the answer choices for perfect squares.
C --> If T = 16, we get 6root(16) = 16 + 8
Simplify to get 24 = 24
Answer = C
Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
-
chieftang
- Master | Next Rank: 500 Posts
- Posts: 218
- Joined: Wed Nov 23, 2011 8:05 pm
- Thanked: 26 times
- Followed by:4 members
Pretty good question.
I ended up with a quadratic eqn T^2 - 20T + 64 = 0, factored to (T-16)(T-4)=0, and threw out the soln 4 without further thought since it wasn't an answer choice. Interestingly, though, that soln is the weight... But that left me with T=16 for the age. Answer C
I ended up with a quadratic eqn T^2 - 20T + 64 = 0, factored to (T-16)(T-4)=0, and threw out the soln 4 without further thought since it wasn't an answer choice. Interestingly, though, that soln is the weight... But that left me with T=16 for the age. Answer C
-
ronnie1985
- Legendary Member
- Posts: 626
- Joined: Fri Dec 23, 2011 2:50 am
- Location: Ahmedabad
- Thanked: 31 times
- Followed by:10 members
If the age of T is x then weight is √x.
The given conditions can be converted into the equation,
√(2x+17) - 3 = √x
Solving we get x = 16 or 4
Since T is teenager, he is 16 years of age.
The given conditions can be converted into the equation,
√(2x+17) - 3 = √x
Solving we get x = 16 or 4
Since T is teenager, he is 16 years of age.
Follow your passion, Success as perceived by others shall follow you
-
GMATGuruNY
- GMAT Instructor
- Posts: 15539
- Joined: Tue May 25, 2010 12:04 pm
- Location: New York, NY
- Thanked: 13060 times
- Followed by:1906 members
- GMAT Score:790
ALWAYS LOOK AT THE ANSWER CHOICES.neelgandham wrote:A Trussian's weight, in keils, can be calculated by taking the square root of his age in years. A Trussianteenager now weighs three keils less than he will seventeen years after he is twice as old as he is now. How old is he now?
(A) 14 (B) 15 (C) 16 (D) 17 (E) 18
Source: A local-GMAT-prep-company's material
When a GMAT question involves a real-world situation, the implied values will be realistic.
The number of dogs sold will be an integer; the weight of a person will not be a radical.
How could a scale in the real world register a weight of 10√2 or 8√3?
Thus, since the current weight of the teenager is the square root of the correct answer, the only viable answer choice here is C.
The correct answer is C.
If we wanted to be very, very safe, we could quickly plug in answer choice C:
Current weight = √16 = 4.
17 years after he is twice as old = 17 + 2*16 = 49, implying a weight of 7.
Weight difference = 7-4 = 3.
Success!
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
-
hazelnut01
- Master | Next Rank: 500 Posts
- Posts: 157
- Joined: Sat Nov 19, 2016 5:34 am
- Thanked: 2 times
- Followed by:4 members
Let us call the Trussian's current age a. Why my equation incorrect? 17−3√a=2a?neelgandham wrote:A Trussian's weight, in keils, can be calculated by taking the square root of his age in years. A Trussian teenager now weighs three keils less than he will seventeen years after he is twice as old as he is now. How old is he now?
(A) 14 (B) 15 (C) 16 (D) 17 (E) 18
Source: Manhattan Challenge Problems (2002, October 7 - Weighty Years)
GMAT/MBA Expert
-
[email protected]
- Elite Legendary Member
- Posts: 10392
- Joined: Sun Jun 23, 2013 6:38 pm
- Location: Palo Alto, CA
- Thanked: 2867 times
- Followed by:511 members
- GMAT Score:800
Hi ziyuenlau,
This question can be solved rather easily by TESTing THE ANSWERS. If you're going to approach it algebraically though, then you have to be careful about whether your variables are referring to age OR weight.
According to the prompt, age is in YEARS and weight is in SQUARE-ROOT of YEARS.
For example:
X = age (in years)
√X = weight (in kiels)
The phrase "A Trussian teenager now WEIGHS three keils less than he will seventeen years after he is twice as old as he is now" focuses on the current WEIGHT relative to a future WEIGHT, so we're going to need a couple of square-root signs. It translates into:
√X = √(2X+17) - 3
GMAT assassins aren't born, they're made,
Rich
This question can be solved rather easily by TESTing THE ANSWERS. If you're going to approach it algebraically though, then you have to be careful about whether your variables are referring to age OR weight.
According to the prompt, age is in YEARS and weight is in SQUARE-ROOT of YEARS.
For example:
X = age (in years)
√X = weight (in kiels)
The phrase "A Trussian teenager now WEIGHS three keils less than he will seventeen years after he is twice as old as he is now" focuses on the current WEIGHT relative to a future WEIGHT, so we're going to need a couple of square-root signs. It translates into:
√X = √(2X+17) - 3
GMAT assassins aren't born, they're made,
Rich
