BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Decimals

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pm
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770

by Anurag@Gurome » Sat Nov 12, 2011 4:04 am
shankar.ashwin wrote:If 0.0abababab.... = 2/55, then what is the value of a*b?
2/55 = (2000/55)/1000

Now, 2000/55 = 400/11 = 36.36...
Hence, 2/55 = (36.36...)/1000 = 0.03636...

Comparing this with the expression given, a = 3 and b = 6

Therefore, a*b = 3*6 = 18
[spoiler]
The correct answer is B.[/spoiler]
Last edited by Anurag@Gurome on Sat Nov 12, 2011 4:36 am, edited 1 time in total.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pm
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770

by Anurag@Gurome » Sat Nov 12, 2011 4:08 am
Another Approach:
If someone is fast enough to do the division and see the pattern they can go for the traditional approach of attacking recurring decimal problems.

--> 0.0abababab... = 2/55
--> 10*(0.0abababab...) = 0.abababab... = 20/55 .............. (1)
--> 1000*(0.0abababab...) = ab.abababab... = 2000/55 ....... (2)

Subtracting (1) from (2), ab = 1980/55 = 36

Hence, a = 3 and b = 2
Therefore, a*b = 3*6 = 18
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
Top
Legendary Member
Posts: 966
Joined: Sat Jan 02, 2010 8:06 am
Thanked: 230 times
Followed by:21 members

by shankar.ashwin » Sat Nov 12, 2011 4:26 am
The way i did it,

2/55 = x/100

x = 200/55 = 40/11 = 3.6363..

Wasnt sure if it was the fastest way to do it.
Top
Master | Next Rank: 500 Posts
Posts: 385
Joined: Fri Sep 23, 2011 9:02 pm
Thanked: 62 times
Followed by:6 members

by user123321 » Sat Nov 12, 2011 5:17 am
2/55 = 4/110 = 36/990 = 3.6/99 = 0.0363636
so 3*6 = 18

user123321
Just started my preparation :D
Want to do it right the first time.
Top
Senior | Next Rank: 100 Posts
Posts: 44
Joined: Wed Aug 25, 2010 12:23 am
Thanked: 6 times

by rooster » Mon Nov 14, 2011 2:56 am
2/55= 0.036

We know the pattern is .0ababababa....

Thus we already know. multiply 3*6 and presto!
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 359
Joined: Wed Mar 11, 2009 4:37 am
Location: Kolkata, India
Thanked: 50 times
Followed by:2 members

by Abhishek009 » Mon Nov 14, 2011 7:22 am
shankar.ashwin wrote:If 0.0abababab.... = 2/55, then what is the value of a*b?

A) 10
B) 18
C) 27
D) 36
E) 42
2/55 => 2/( 5 * 11 )

2/5 = 0.4

Again we have 0.4/11


We know 1/11 => 0.09090909.....{ We can memorize some key reciprocals till 1/20 for quicker calculations}


So, 0.4/11 => 0.09090909..... * 0.4 => 0.036363636363636.....


Here a = 3 and b = 6

So , a * b => 3 * 6 = 18...
Abhishek
Top
Post new topic Post Reply
• Page 1 of 1