Last visit was: 19 Nov 2025, 01:17 It is currently 19 Nov 2025, 01:17
Home
GMAT
Messages
Tests
Schools
Events
Rewards
Chat
My Profile
Close
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
Your Progress

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
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
Back to Forum
Create Topic
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,379
Own Kudos:
778,165
 [3]
Given Kudos: 99,977
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,379
Kudos: 778,165
 [3]
'a' and 'b' are positive integers such that their LCM is 20 and their 31 Jan 2022, 04:45
Kudos
Add Kudos
3
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

55% (hard)

Question Stats:

60% (01:26) correct 40% (01:43) wrong based on 241 sessions

History

Date
Time
Result
Not Attempted Yet
'a' and 'b' are positive integers such that their LCM is 20 and their HCF is 1. What is the difference between the maximum and minimum possible values of 'a + b'?

A. 0
B. 9
C. 11
D. 12
E. 13


Are You Up For the Challenge: 700 Level Questions
ShowHide Answer
Official Answer
D
User avatar
JerryAtDreamScore
User avatar
Dream Score Representative
Joined: 07 Oct 2021
Last visit: 02 Jul 2022
Posts: 380
Own Kudos:
417
 [2]
Given Kudos: 2
Posts: 380
Kudos: 417
 [2]
'a' and 'b' are positive integers such that their LCM is 20 and their 31 Jan 2022, 17:18
2
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
'a' and 'b' are positive integers such that their LCM is 20 and their HCF is 1. What is the difference between the maximum and minimum possible values of 'a + b'?

A. 0
B. 9
C. 11
D. 12
E. 13

Show more

Breaking Down the Info:

HCF (highest common factor) = 1 tells us a and b have no common factors.

The LCM is 20, so we need to break down 20 into two unrelated integers.

One way would be 20 = 4*5, which created the smallest value of a + b. The biggest value we can have is from 20 = 20*1.

Thus the maximum value of a + b is 21, the minimum is 9. The difference is 21 - 9 = 12.

Answer: D
User avatar
Adiyogi123
User avatar
Joined: 26 Jun 2023
Last visit: 20 Aug 2025
Posts: 3
Own Kudos:
1
Given Kudos: 45
Posts: 3
Kudos: 1
'a' and 'b' are positive integers such that their LCM is 20 and their 11 Apr 2025, 02:19
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Why can a and b be equal ?
a= 40 and b = 40 and a= 1 and b = 1 ?
So Max value a+b would be 40 and min value would be 1


Diff = 39 ?
JerryAtDreamScore
Bunuel
'a' and 'b' are positive integers such that their LCM is 20 and their HCF is 1. What is the difference between the maximum and minimum possible values of 'a + b'?

A. 0
B. 9
C. 11
D. 12
E. 13


Breaking Down the Info:

HCF (highest common factor) = 1 tells us a and b have no common factors.

The LCM is 20, so we need to break down 20 into two unrelated integers.

One way would be 20 = 4*5, which created the smallest value of a + b. The biggest value we can have is from 20 = 20*1.

Thus the maximum value of a + b is 21, the minimum is 9. The difference is 21 - 9 = 12.

Answer: D
Show more
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,379
Own Kudos:
778,165
Given Kudos: 99,977
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,379
Kudos: 778,165
'a' and 'b' are positive integers such that their LCM is 20 and their 11 Apr 2025, 02:57
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Adiyogi123
Why can a and b be equal ?
a= 40 and b = 40 and a= 1 and b = 1 ?
So Max value a+b would be 40 and min value would be 1


Diff = 39 ?
JerryAtDreamScore
Bunuel
'a' and 'b' are positive integers such that their LCM is 20 and their HCF is 1. What is the difference between the maximum and minimum possible values of 'a + b'?

A. 0
B. 9
C. 11
D. 12
E. 13


Breaking Down the Info:

HCF (highest common factor) = 1 tells us a and b have no common factors.

The LCM is 20, so we need to break down 20 into two unrelated integers.

One way would be 20 = 4*5, which created the smallest value of a + b. The biggest value we can have is from 20 = 20*1.

Thus the maximum value of a + b is 21, the minimum is 9. The difference is 21 - 9 = 12.

Answer: D
Show more

If a = b = 40, the LCM of 40 and 40 is 40, not 20, and the HCF of 40 and 40 is also 40, not 1.
If a = b = 1, the LCM of 1 and 1 is 1, not 20.
Moderators:
Bunuel
Math Expert
105379 posts
Krunaal
Tuck School Moderator
805 posts