Last visit was: 11 Aug 2026, 14:05 It is currently 11 Aug 2026, 14:05
Home
Messages
Tests
Schools
Events
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
   1   2 
User avatar
KarishmaB
User avatar
Joined: 16 Oct 2010
Last visit: 11 Aug 2026
Posts: 16,597
Own Kudos:
80,750
 [1]
Given Kudos: 488
Location: Pune, India
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 16,597
Kudos: 80,750
 [1]
Machine A takes 2 more hours than machine B to make 20 widgets. If wor 11 Nov 2020, 01:14
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
plaverbach
VeritasKarishma , thanks for the insights!

I came with an approach that I could not follow throw, can any one point me in the wright direction?

I tried to make sure that I was working with just one full work, and I thought that 100 widgets was a good number.

So A would take 10 more hours than machine B to make 100 widgets
AND
Working together, the machines can make 100 widgets in 12 hours

QUESTION
how long will it take machine A to make 40 widgets

Was this a good approach? How can one solve it?

[edit] I could solve in ~10 min, but this was not a good idea, right?
Show more

Yes, you can make the work same so that you don't have to worry about it. But to ensure that all numbers remain integers, I would take the work to be 200 hrs (LCM of 20, 25 and 40).

A will take 20 more hrs than B working alone to do this work.
Working together the work is done in 24 hrs.

1/A + 1/(A-20) = 1/24
From here, we will get time taken by A to make 200 widgets.

Options give us time taken by A to make 40 widgets. So we will check each option multiplied by 5 in our equation.
If you plug in (E) * 5 = 12*5 = 60 in the equation, you get

1/60 + 1/40 = 1/24 which is correct.
User avatar
Natansha
User avatar
Joined: 13 Jun 2019
Last visit: 11 Mar 2026
Posts: 195
Own Kudos:
66
Given Kudos: 84
Posts: 195
Kudos: 66
Machine A takes 2 more hours than machine B to make 20 widgets. If wor 04 Sep 2025, 04:18
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Hi KarishmaB I have a doubt in selecting the number for denominator as well.

We have 40/x + 40/(x-4) = 25/3 , we need a value of x such that we can get a 3 in the denominator but every ans opt other than 5 will give us that:

6 will give x = 6 and x-4 = 2, with LCM = 6 (multiple of 3)
8 will give x=8 & x-4 = 4 with LCM = 24 (multiple of 3)
10 will give x = 10 & x-4 = 6, LCM = 60 (multiple of 3)
12 will give x = 12 & x-4 = 8, LCM= 24 (multiple of 3)

so unless we put each options fully and solve, how are we supposed to narrow down the options?

KarishmaB


Try this:

a + b = 25/3

Which two numbers without a denominator of 3 can you add to give 25/3? There needs to be a 3 in the denominator in at least one of a or b to get the sum of 25/3.

Similarly try a + b = 11/2
11/2 is 5.5. So the 0.5 has to come from somewhere to add up to 5.5
Show more
User avatar
KarishmaB
User avatar
Joined: 16 Oct 2010
Last visit: 11 Aug 2026
Posts: 16,597
Own Kudos:
80,750
Given Kudos: 488
Location: Pune, India
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 16,597
Kudos: 80,750
Machine A takes 2 more hours than machine B to make 20 widgets. If wor 04 Sep 2025, 07:02
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Simplify it fully first.

1/x + 1/(x-4) = 25/3*40

1/x + 1/(x-4) = 5/24

Possible option x = 12. No other option gives 3 and 8 as factors.

Or

Note that 25/3 = 8.something
40/x + 40/(x-4) = 25/3

If x = 6, 40/2 is much greater than 8.
If x = 8, 40/4 = 10 i.e. greater than 8
If x = 10, 40/10 + 40/6 is greater than 8



Natansha
Hi KarishmaB I have a doubt in selecting the number for denominator as well.

We have 40/x + 40/(x-4) = 25/3 , we need a value of x such that we can get a 3 in the denominator but every ans opt other than 5 will give us that:

6 will give x = 6 and x-4 = 2, with LCM = 6 (multiple of 3)
8 will give x=8 & x-4 = 4 with LCM = 24 (multiple of 3)
10 will give x = 10 & x-4 = 6, LCM = 60 (multiple of 3)
12 will give x = 12 & x-4 = 8, LCM= 24 (multiple of 3)

so unless we put each options fully and solve, how are we supposed to narrow down the options?


Show more
User avatar
Ngocanhvy
User avatar
Joined: 11 Aug 2024
Last visit: 14 Jun 2026
Posts: 21
Own Kudos:
4
Given Kudos: 38
Posts: 21
Kudos: 4
Machine A takes 2 more hours than machine B to make 20 widgets. If wor 07 Sep 2025, 03:42
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Let's call t as the number of hours that A need to complete 40 widget.
So A needs t/2 hours to complete 20 widget
and B needs (t-4)/2 hours to complete 20 widget

So to complete 25 widget:
A needs: t/2 * (25/20) = 5t/8 hours
B needs: (t-4)/2 * (25/20) = 5(t-4)/8 hours

Work done by A * B in hours as below:
8/5t + 8/(5t-4) = 1/3
Multiple both sides with 5/8, we have:
1/t - 1/(t-4) = 5/24

Now you can start plugging number. I often started with finding 2 numbers with common mutiple is 24, and the difference between them is 4. Eg: 12 vs 8 are satisfied
1/12 + 1/8 = 5/24.
Bingo!! the answer is 12!

You can read more about this solution via the post named Evading calculation (written by Karishma, reposted by Bunuel)
User avatar
MrMaxMan
User avatar
Joined: 13 Jul 2026
Last visit: 11 Aug 2026
Posts: 35
Own Kudos:
1
Given Kudos: 41
Posts: 35
Kudos: 1
Machine A takes 2 more hours than machine B to make 20 widgets. If wor 31 Jul 2026, 16:54
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Ra + Rb = 25/3
20/x + 20/(x-2) = 25/3

How long (t) will it take machine (a) alone to produce 40?
40/t = Ra
Ra = 20/x
The answer will be the choice where both are true. Test out the answer choices. I like to start in the middle and move up or down depending on result.

if t=12
then Ra = 40/12 = 20/6 = 10/3
if 10/3 = 20/x, 10x=60, x=6
if x=6 and 20/x + 20/(x-2) = 25/3
then t=12 is correct.
20/6 + 20/(6-2) = 20/6 + 20/4 = 40/12 + 60/12 = 100/12 = 25/3 which is true with our earlier equation.
Since 25/3=25/3 we know x to be true and therefore t=12 to be true.
   1   2 
Moderator:
Bunuel
Math Expert
112650 posts