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Edu and Fran are bricklayers. Working alone, Edu could build 21 Apr 2026, 12:29
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Edu and Fran are bricklayers. Working alone, Edu could build a certain wall in 12 hours and Fran could build it in 10 hours. Working together, they lay 90 more bricks per hour than they would if they worked separately. If they complete the wall in 3 hours, how many bricks does it contain?

(A) 480
(B) 540
(C) 600
(D) 660
(E) 720
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C
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Edu and Fran are bricklayers. Working alone, Edu could build 21 Apr 2026, 21:28
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Number of bricks in the wall = w.

Then,

Edu's rate of work when working individually = w/12.
Fran's rate of work when working individually = w/10.

If they had worked separately, in one hour, they would have laid (w/12 + w/10) bricks in an hour.

We are given that working together, they laid 90 more bricks per hour than the above.

So,

Number of bricks laid per hour by both, working together = w/12 + w/10 + 90.

They completed the work in 3 hours.

Hence,

(w/12 + w/10 + 90) x 3 = total number of bricks in the wall = w.

Simplifying the above, we get w = 600. Choice C.

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Edu and Fran are bricklayers. Working alone, Edu could build 06 Jul 2026, 05:45
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Hi @hashavardhanR

Could you please explain a point on this quesiton.

While i understand the solution, this part of the language below is not clear to me

"Working together, they lay 90 more bricks per hour than they would if they worked separately"

How sum of working separately for the same time be different from the sum of working together for the same time. Say if A is making x units per hour and B is making y units per hour then together they will make x + y units per hour. Which is the same as if you add up their individual productions which is add separately x and separately y.

Request you to please help.


HarshavardhanR
Number of bricks in the wall = w.

Then,

Edu's rate of work when working individually = w/12.
Fran's rate of work when working individually = w/10.

If they had worked separately, in one hour, they would have laid (w/12 + w/10) bricks in an hour.

We are given that working together, they laid 90 more bricks per hour than the above.

So,

Number of bricks laid per hour by both, working together = w/12 + w/10 + 90.

They completed the work in 3 hours.

Hence,

(w/12 + w/10 + 90) x 3 = total number of bricks in the wall = w.

Simplifying the above, we get w = 600. Choice C.

---
Harsha
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HarshavardhanR
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Edu and Fran are bricklayers. Working alone, Edu could build 06 Jul 2026, 07:03
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Hi Vivek1707,

Great question! This sentence is trickier than it looks (in my view).

"Working together, they lay 90 more bricks per hour than they would if they worked separately"
If they worked individually/separately on laying the bricks of the wall, then, in 1 hour ->

- Edu would lay w/12 bricks
- Fran would lay w/10 bricks
- Together, working separately, they would lay w/12 + w/10 bricks.

To answer your question - "How can the sum of working separately for the same time be different from the sum of working together for the same time"?

Here is an example scenario --- when working individually, a worker has to pick up a brick in one hand, take a bit of cement in the other hand, keep the cement-water mix wet enough for application, spread cement at the spot where the brick will be fixed, and then fix the brick firmly in place.

Perhaps --- now that Edu and Fran are working together, they specialize i.e., they do specific tasks. For example - Edu will pick up the brick and fix the brick in place, whereas Fran will handle all cement-specific tasks. Hence, together, they become more efficient and are able to lay 90 more bricks.

The above is just an example. But yes - this is very real-life. Quite often, while individually, we take time to do an activity, when we team up, we are able to do the same activity more efficiently (or even more effectively). This could be because of a better workflow/process.

Hope you see the logic here.

Thus, working together, the two are able to lay w/12 + w/10 + 90 bricks.

Cheers,
Harsha


Vivek1707
Hi @hashavardhanR

Could you please explain a point on this quesiton.

While i understand the solution, this part of the language below is not clear to me

"Working together, they lay 90 more bricks per hour than they would if they worked separately"

How sum of working separately for the same time be different from the sum of working together for the same time. Say if A is making x units per hour and B is making y units per hour then together they will make x + y units per hour. Which is the same as if you add up their individual productions which is add separately x and separately y.

Request you to please help.



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Edu and Fran are bricklayers. Working alone, Edu could build 06 Jul 2026, 07:12
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Thank you HarshavardhanR for the response this was really helpful.

What I understand is that the question is implying that the productivity of individual workers is increasing when they are working together. While in most of the work rates question I have done such synergies are usually mentioned otherwise the the rates are kept constant, here now I see that the language is implying the increase in synergy otherwise the wording wouldnt make sense.

Thank you again.

HarshavardhanR
Hi Vivek1707,

Great question! This sentence is trickier than it looks (in my view).

"Working together, they lay 90 more bricks per hour than they would if they worked separately"
If they worked individually/separately on laying the bricks of the wall, then, in 1 hour ->

- Edu would lay w/12 bricks
- Fran would lay w/10 bricks
- Together, working separately, they would lay w/12 + w/10 bricks.

To answer your question - "How can the sum of working separately for the same time be different from the sum of working together for the same time"?

Here is an example scenario --- when working individually, a worker has to pick up a brick in one hand, take a bit of cement in the other hand, keep the cement-water mix wet enough for application, spread cement at the spot where the brick will be fixed, and then fix the brick firmly in place.

Perhaps --- now that Edu and Fran are working together, they specialize i.e., they do specific tasks. For example - Edu will pick up the brick and fix the brick in place, whereas Fran will handle all cement-specific tasks. Hence, together, they become more efficient and are able to lay 90 more bricks.

The above is just an example. But yes - this is very real-life. Quite often, while individually, we take time to do an activity, when we team up, we are able to do the same activity more efficiently (or even more effectively). This could be because of a better workflow/process.

Hope you see the logic here.

Thus, working together, the two are able to lay w/12 + w/10 + 90 bricks.

Cheers,
Harsha



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