Roberto has three children: two girls and a boy. All were born on the

Question

Roberto has three children: two girls and a boy. All were born on the same date in different years. The sum of the ages of the two girls today is smaller than the age of the boy today, but a year from now the sum of the ages of the girls will equal the age of the boy. Three years from today, the difference between the age of the boy and the combined ages of the girls will be

A. 1
B. 2
C. 3
D. –2
E. –1

Show Answer

Official Answer

D

A. 1
B. 2
C. 3
D. –2
E. –1

PareshGmat · Accepted Answer

Approach I (Plugin's)

Girl I ............... Girl II ................ Boy

1 ....................... 1 ........................ 3 (Assume the current ages)

1 + 1 < 3 .......... (Satisfies the given condition)

1 Year later there ages are

2 ....................... 2 ......................... 4

2 + 2 = 4 ............ (Satisfies the given condition)

After 3 years there ages are

4 ....................... 4 ............................ 6

Difference = 6 - (4+4) = 6 - 8 = -2

Answer = D

Approach II (Arithmetic)

Girl I ................. Girl II ............... Boy

a ........................ b ...................... c (Assume there current ages; a+b < c)

a+1 ................... b+1 ................... c+1 (Ages after 1 year)

Given that a+1 + b+1 = c+1

a+b = c - 1 ................... (1)

a+3 .................... b+3 .................. c+3 (Ages 3 years later from today)

Difference = c+3 - (a+3+b+3)

= c + 3 - (c-1+6) ............  Substitute from (1)

= 3 - 5 = -2

Answer = D

Bunuel · Answer

Check other  Age Problems HERE .

Infxel · Answer

girl1: g1, girl2: g2, boy:b, these are the symbols for their ages today. g1+g2

gracie · Answer

one year from now, G+g=b
two years after that, G+2+g+2=b+2
➡G+g-b=2-4=-2

CounterSniper · Answer

let g1 and g2 denote age of the girls
now,
as per the question
g1+g2 < b1 --- now
g1+g2+2 = b1+1 (one year from today) ---1

3 years from today the combined age of the girls is
g1+g2+6 
or,
g1+g2+6 = b1+1+4 (substituting the value from 1)

difference = b1+3 - (b1+5) = -2

anairamitch1804 · Answer

Each year, the age of the boy increases by 1. Each year, the sum of the ages of the two girls increases by 2 (as each girl gets older by one year, and there are two of them).
Let's say that the age of the boy today is equal to x, while the combined ages of the girls today is equal to y.
Then, next year the figures will be x + 1 and y + 2, respectively. The problem states that these two figures will be equal, which yields the following equation:

x + 1 = y + 2 which can be simplified to x = y + 1

(This is consistent with the fact that the sum of the ages of the two girls today is smaller than the age of the boy today.)
Three years from now, the combined age of the girls will be y + 3(2) = y + 6. Three years from now, the boy's age will be x + 3. Using the fact (from above) that x = y + 1, the boy's age three years from now can be written as x + 3 = (y + 1) + 3 = y + 4.
The problem asks for the difference between the age of the boy three years from today and the combined ages of the girls three years from today. This difference equals y + 4 – (y + 6) = –2.
The correct answer is D.

Plug in real numbers to see if this makes sense.
Let the girls be 4 and 6 in age. The sum of their ages today is 10. The boy's age today is then (10 + 1) = 11. Three years from today, the girls will be 7 and 9 respectively, so their combined age will be 16. Three years from today, the boy will be 14.

stne · Answer

When it says " Difference" between the boys age and girls age does it necessarily mean Boys age - Girls Age or can it also mean Girls age - Boys age .
For example : Difference between A and B does it necessarily mean A-B or can it mean B-A too!
Hence if we go (Girl 1 + Girl 2) - Boy = 2
But if we go Boy - ( Girl 1 + Girl 2)= -2 
So how are we sure that the latter is being asked here ?

EMPOWERgmatRichC · Answer

Hi All,

This question can be solved rather easily by TESTing VALUES. It is oddly-worded though and not written in the 'style' that Official GMAT questions is written in. I'm going to deal with the information in a slightly out-of-order fashion...

We're told that A YEAR FROM NOW the sum of the ages of the two girls will equal the age of the boy...

IF.... in ONE YEAR.... 
1st Girl = 2 
2nd Girl = 3 
Boy = 5

Right NOW... 
1st Girl = 1 
2nd Girl = 2 
Boy = 4

Three years from NOW... 
1st Girl = 1+3 = 4 
2nd Girl = 2+3 = 5 
Boy = 4+3 = 7

Thus, in three years, the difference between the sum of the girls ages (9) and the age of the boy (7) is 2. The author of the prompt wants us to subtract the sum of the girls' ages from the age of the boy, but the author uses the word "difference", which in conventional terms is always considered a positive number (e.g. the difference in points scored by two sports teams is "2 points", not "-2 points"). If this question appeared on the Official GMAT, and we were meant to choose the listed correct answer D, then the prompt would have stated something to the effect of "In three years, the age of the boy minus the sum of the ages of the two girls would be...?"

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

jasmeet447 · Answer

But the difference between any two numbers is always considered a positive number. is -2 correct for the solution or it'll be "2". Please explain

firas92 · Answer

Not true. The question should explicitly mention "positive difference" for us consider the difference between the two numbers as positive

Posted from my mobile device

kornn · Answer

Dear  IanStewart ,

I nearly picked B. as an answer.
From your experience, the difference between A and B ALWAYS MEANS A - B. 
Or it could mean B - A?

I tend to take the difference as an absolute value.

IanStewart · Answer

The meaning is ambiguous. It's not an official question, and an official question wouldn't be worded this way.

Aishyk97 · Answer

Hi  PareshGmat ,
I think there is a problem with your first approach. The ages of both girls cannot be the same. You have taken each of their ages as 1 or 2. The question stem states that each of the children was born on the same date but in different years.

Please correct me if I am wrong.

Bunuel

bumpbot · Answer

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Roberto has three children: two girls and a boy. All were born on the

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