If Father's age is 1 less than twice the son's age, what is : GMAT Data Sufficiency (DS)
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 17 Jan 2017, 19:20

### 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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# If Father's age is 1 less than twice the son's age, what is

Author Message
TAGS:

### Hide Tags

Intern
Joined: 17 Jan 2012
Posts: 41
GMAT 1: 610 Q43 V31
Followers: 1

Kudos [?]: 145 [3] , given: 16

If Father's age is 1 less than twice the son's age, what is [#permalink]

### Show Tags

31 Jan 2012, 03:50
3
KUDOS
11
This post was
BOOKMARKED
00:00

Difficulty:

95% (hard)

Question Stats:

55% (03:06) correct 45% (02:15) wrong based on 212 sessions

### HideShow timer Statistics

If Father's age is 1 less than twice the son's age, what is the son's age?

(1) The digits MN making up the father's age are reversed in the son's age i.e NM.
(2) Father is at least 25 years older than son

I m not sure of the answer but i think its "A"

Gimme Kudos if you like the question
[Reveal] Spoiler: OA

Last edited by docabuzar on 31 Jan 2012, 12:24, edited 1 time in total.
Math Expert
Joined: 02 Sep 2009
Posts: 36540
Followers: 7072

Kudos [?]: 93041 [7] , given: 10541

Re: Father & Son Age [#permalink]

### Show Tags

31 Jan 2012, 05:02
7
KUDOS
Expert's post
4
This post was
BOOKMARKED
docabuzar wrote:
If Father's age is 1 less than twice the son's age, what is the son's age?
A. The digits MN making up the father's age are reversed in the son's age i.e NM.
B. Father is at least 25 years older than son

I m not sure of the answer but i think its "A"

Given: F+1=2S. Question: S=?

(1) The digits MN making up the father's age are reversed in the son's age i.e NM --> F=10M+N and S=10N+M (notice that M and N must be digits: 0, 1, 2, ..., 9) --> (10M+N)+1=2*(10N+M) --> 8M=19N-1. Only one set of digits satisfy this equation: M=7 and N=3 (by trial and error: 19N-1 is even and also a multiple of 8 --> N must odd --> so try N=1 and N=3 to see whether 19N-1 is a multiple of 8. For N>=5, M>10 so not a solution for M as it must be a single digit integer) --> S=10N+M=37 and F=73. Sufficient.

(2) Father is at least 25 years older than son. Clearly insufficient: S=25 and N=13 or S=27 and N=14 .

Hope it's clear.
_________________
Manager
Status: MBA Aspirant
Joined: 12 Jun 2010
Posts: 178
Location: India
WE: Information Technology (Investment Banking)
Followers: 3

Kudos [?]: 79 [0], given: 1

Re: Father & Son Age [#permalink]

### Show Tags

31 Jan 2012, 20:31
Bunuel wrote:
docabuzar wrote:
If Father's age is 1 less than twice the son's age, what is the son's age?
A. The digits MN making up the father's age are reversed in the son's age i.e NM.
B. Father is at least 25 years older than son

I m not sure of the answer but i think its "A"

Given: F+1=2S. Question: S=?

(1) The digits MN making up the father's age are reversed in the son's age i.e NM --> F=10M+N and S=10N+M (notice that M and N must be digits: 0, 1, 2, ..., 9) --> (10M+N)+1=2*(10N+M) --> 8M=19N-1. Only one set of digits satisfy this equation: M=7 and N=3 (by trial and error: 19N-1 is even and also a multiple of 8 --> N must odd --> so try N=1 and N=3 to see whether 19N-1 is a multiple of 8. For N>=5, M>10 so not a solution for M as it must be a single digit integer) --> S=10N+M=37 and F=73. Sufficient.

(2) Father is at least 25 years older than son. Clearly insufficient: S=25 and N=13 or S=27 and N=14 .

Hope it's clear.

Bunnel: will the equation here not be F-1 =2S ( Father's age is 1 less than twice the son's age)
Intern
Joined: 17 Jan 2012
Posts: 41
GMAT 1: 610 Q43 V31
Followers: 1

Kudos [?]: 145 [0], given: 16

Re: If Father's age is 1 less than twice the son's age, what is [#permalink]

### Show Tags

31 Jan 2012, 21:00
Its all in the wording. Father is 1 less than twice of son, so in other words twice of son is 1 more than father

F = 2S -1

Had it been like " Father is 1 more than twice the son " then F=2S+1 or F-1=2S.

Hope I have added some thing.
Manager
Status: MBA Aspirant
Joined: 12 Jun 2010
Posts: 178
Location: India
WE: Information Technology (Investment Banking)
Followers: 3

Kudos [?]: 79 [0], given: 1

Re: If Father's age is 1 less than twice the son's age, what is [#permalink]

### Show Tags

31 Jan 2012, 23:05
docabuzar wrote:
Its all in the wording. Father is 1 less than twice of son, so in other words twice of son is 1 more than father

F = 2S -1

Had it been like " Father is 1 more than twice the son " then F=2S+1 or F-1=2S.

Hope I have added some thing.

Hey thanks for the explanation. I just messed up with the words.
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7119
Location: Pune, India
Followers: 2131

Kudos [?]: 13631 [2] , given: 222

Re: If Father's age is 1 less than twice the son's age, what is [#permalink]

### Show Tags

01 Feb 2012, 01:26
2
KUDOS
Expert's post
1
This post was
BOOKMARKED
docabuzar wrote:
If Father's age is 1 less than twice the son's age, what is the son's age?
A. The digits MN making up the father's age are reversed in the son's age i.e NM.
B. Father is at least 25 years older than son

I m not sure of the answer but i think its "A"

Gimme Kudos if you like the question

Look at the big picture. You can solve this question quickly using intuition.

Father's age is almost as much as twice of son's age. (just 1 less)
Son's age = NM, Father's age = MN

Say, son's age is 12 then father's is 21 (3 less than twice)
Say, son's age is 13 then father's is 31 (much more than twice)
I hope you understand that you can give up on the 10s series here because the gap will keep widening (diff b/w 14 and 41 will be even more)

Say, son's age is 24 then father's is 42 (much less than twice)
Say, son's age is 25, then father's is 52 (more than twice so give up on the 20s series too)

Say son's age is 36, then father's is 63 (much less than twice)
Say son's age is 37, then father's is 73 (1 less than twice. Got it!)

It's easy to say that there will be no other such combination because 49, 94 doesn't work. Nothing in 50s, 60s and so on will work because we need to stick to 2 digit numbers.

Hence, only statement 1 is sufficient.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for \$199

Veritas Prep Reviews

Math Expert
Joined: 02 Sep 2009
Posts: 36540
Followers: 7072

Kudos [?]: 93041 [0], given: 10541

Re: Father & Son Age [#permalink]

### Show Tags

01 Feb 2012, 01:30
subhajeet wrote:
Bunuel wrote:
docabuzar wrote:
If Father's age is 1 less than twice the son's age, what is the son's age?
A. The digits MN making up the father's age are reversed in the son's age i.e NM.
B. Father is at least 25 years older than son

I m not sure of the answer but i think its "A"

Given: F+1=2S. Question: S=?

(1) The digits MN making up the father's age are reversed in the son's age i.e NM --> F=10M+N and S=10N+M (notice that M and N must be digits: 0, 1, 2, ..., 9) --> (10M+N)+1=2*(10N+M) --> 8M=19N-1. Only one set of digits satisfy this equation: M=7 and N=3 (by trial and error: 19N-1 is even and also a multiple of 8 --> N must odd --> so try N=1 and N=3 to see whether 19N-1 is a multiple of 8. For N>=5, M>10 so not a solution for M as it must be a single digit integer) --> S=10N+M=37 and F=73. Sufficient.

(2) Father is at least 25 years older than son. Clearly insufficient: S=25 and N=13 or S=27 and N=14 .

Hope it's clear.

Bunnel: will the equation here not be F-1 =2S ( Father's age is 1 less than twice the son's age)

It's all about word translation: father's age is 1 less than twice the son's age, so F is less than 2S by 1 --> so we need to add 1 to F to get 2S --> F+1=2S.

Hope it's clear
_________________
GMAT Club Legend
Joined: 09 Sep 2013
Posts: 13434
Followers: 575

Kudos [?]: 163 [0], given: 0

Re: If Father's age is 1 less than twice the son's age, what is [#permalink]

### Show Tags

02 Oct 2014, 02:10
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.
_________________
GMAT Club Legend
Joined: 09 Sep 2013
Posts: 13434
Followers: 575

Kudos [?]: 163 [0], given: 0

Re: If Father's age is 1 less than twice the son's age, what is [#permalink]

### Show Tags

11 Jan 2016, 01:51
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.
_________________
Intern
Joined: 19 Nov 2016
Posts: 15
Schools: Erasmus '18
Followers: 0

Kudos [?]: 0 [0], given: 6

Re: If Father's age is 1 less than twice the son's age, what is [#permalink]

### Show Tags

23 Dec 2016, 15:08
Bunuel wrote:
docabuzar wrote:
If Father's age is 1 less than twice the son's age, what is the son's age?
A. The digits MN making up the father's age are reversed in the son's age i.e NM.
B. Father is at least 25 years older than son

I m not sure of the answer but i think its "A"

Given: F+1=2S. Question: S=?

(1) The digits MN making up the father's age are reversed in the son's age i.e NM --> F=10M+N and S=10N+M (notice that M and N must be digits: 0, 1, 2, ..., 9) --> (10M+N)+1=2*(10N+M) --> 8M=19N-1. Only one set of digits satisfy this equation: M=7 and N=3 (by trial and error: 19N-1 is even and also a multiple of 8 --> N must odd --> so try N=1 and N=3 to see whether 19N-1 is a multiple of 8. For N>=5, M>10 so not a solution for M as it must be a single digit integer) --> S=10N+M=37 and F=73. Sufficient.

(2) Father is at least 25 years older than son. Clearly insufficient: S=25 and N=13 or S=27 and N=14 .

Hope it's clear.

Hello can you elaborate if it is possible? how did we come up with F=10M+N and S=10N+M , Basically i understood how u solved it but i cannot comprehend the way we approach it initially

Math Expert
Joined: 02 Sep 2009
Posts: 36540
Followers: 7072

Kudos [?]: 93041 [0], given: 10541

Re: If Father's age is 1 less than twice the son's age, what is [#permalink]

### Show Tags

23 Dec 2016, 23:55
stampap wrote:
Bunuel wrote:
docabuzar wrote:
If Father's age is 1 less than twice the son's age, what is the son's age?
A. The digits MN making up the father's age are reversed in the son's age i.e NM.
B. Father is at least 25 years older than son

I m not sure of the answer but i think its "A"

Given: F+1=2S. Question: S=?

(1) The digits MN making up the father's age are reversed in the son's age i.e NM --> F=10M+N and S=10N+M (notice that M and N must be digits: 0, 1, 2, ..., 9) --> (10M+N)+1=2*(10N+M) --> 8M=19N-1. Only one set of digits satisfy this equation: M=7 and N=3 (by trial and error: 19N-1 is even and also a multiple of 8 --> N must odd --> so try N=1 and N=3 to see whether 19N-1 is a multiple of 8. For N>=5, M>10 so not a solution for M as it must be a single digit integer) --> S=10N+M=37 and F=73. Sufficient.

(2) Father is at least 25 years older than son. Clearly insufficient: S=25 and N=13 or S=27 and N=14 .

Hope it's clear.

Hello can you elaborate if it is possible? how did we come up with F=10M+N and S=10N+M , Basically i understood how u solved it but i cannot comprehend the way we approach it initially

This is a way of writing a two-digit number. Any two-digit integer can be represented as 10a+b (where a and b are single digit integers), for example 37=3*10+7, 88=8*10+8, etc.
_________________
Intern
Joined: 19 Nov 2016
Posts: 15
Schools: Erasmus '18
Followers: 0

Kudos [?]: 0 [0], given: 6

Re: If Father's age is 1 less than twice the son's age, what is [#permalink]

### Show Tags

24 Dec 2016, 06:16
Oh yes! silly me , i had completely forgot it , now its clear!

thank you bunuel
Re: If Father's age is 1 less than twice the son's age, what is   [#permalink] 24 Dec 2016, 06:16
Similar topics Replies Last post
Similar
Topics:
What is Mary’s age? 2 14 Feb 2016, 10:13
6 If Tom's age is 5 years less than the combined ages of Dick and Harry, 7 23 Apr 2015, 15:10
2 If Shannon's age is exactly half of Josh's age, what is Shannon's age? 4 12 Feb 2015, 06:05
3 What is Ricky's age now? 6 09 Jan 2014, 05:50
14 If Sara's age is exactly twice Bill's age, what is Sara's ag 8 18 Dec 2012, 06:43
Display posts from previous: Sort by