Really quick brain teaser problem

This topic has expert replies
User avatar
Newbie | Next Rank: 10 Posts
Posts: 2
Joined: Tue Mar 18, 2014 5:45 am

Really quick brain teaser problem

by Coelhothales » Tue Mar 18, 2014 5:47 am
Hey I need help on this problem , does anyone have an idea if there is a correct answer ?

Mike has three children of different ages. How old is the youngest today?
(1) The two older children have, together, 18 years
(2) The two younger children have, together, 7 years

Does it have a possible answer ?

Thanks all !

GMAT/MBA Expert

User avatar
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

by [email protected] » Tue Mar 18, 2014 7:49 pm
Hi Coelhothales,

This is a badly-worded DS question, but the math behind it provides enough information to choose an answer.

We're told that there are three children with different ages. We're asked for the age of the youngest child.

I'm going to call the children...

X = youngest
Y = middle
Z = oldest

Fact 1: Y + Z = 18

This tells us NOTHING about the age of the youngest child.
Fact 1 is INSUFFICIENT

Fact 2: X + Y = 7

We could have...
X = 1, Y = 6
X = 2, Y = 5
X = 3, Y = 4
Since we don't know what age the youngest child actually is...
Fact 2 is INSUFFICIENT

Combined, we run into the same problem that we had with Fact 2: multiple answers.

Y + Z = 18
X + Y = 7

We could have...
X = 1, Y = 6, Z = 12
X = 2, Y = 5, Z = 13
Combined, INSUFFICIENT

Final Answer: E

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
Image

User avatar
MBA Admissions Consultant
Posts: 2279
Joined: Fri Nov 11, 2011 7:51 am
Location: New York
Thanked: 660 times
Followed by:266 members
GMAT Score:770

by Jim@StratusPrep » Tue Apr 01, 2014 8:19 am
The basic thought is you have 3 variables so you will need 3 separate equations to solve for the variables.

*there are rare instances where multiple variables can be cancelled when simplifying expressions, making this rule not a 100% truth. It is an easy check to see that this does not happen in this case.

Again, this is a poorly worded question, so I would look to a different source for material.
GMAT Answers provides a world class adaptive learning platform.
-- Push button course navigation to simplify planning
-- Daily assignments to fit your exam timeline
-- Organized review that is tailored based on your abiility
-- 1,000s of unique GMAT questions
-- 100s of handwritten 'digital flip books' for OG questions
-- 100% Free Trial and less than $20 per month after.
-- Free GMAT Quantitative Review

Image