Jim can assemble b crates in an hour and Robert

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M7MBA: Moderator; Posts: 2058; Joined: Sun Oct 29, 2017 4:24 am; Thanked: 1 times; Followed by:5 members

Jim can assemble b crates in an hour and Robert

by M7MBA » Sun Dec 17, 2017 8:34 am

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Jim can assemble b crates in an hour and Robert can assemble 2b crates in an hour. Working together at this rate, how many crates can they assemble in four hours?

A) 3b

B) 6b

C) 8b

D) 12b

E) 18b

The OA is D.

Which is the equation I should set to solve this PS question? Experts, may you give me some help, please?

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Source: Beat The GMAT — Problem Solving | Sun Dec 17, 2017 8:34 am

EconomistGMATTutor: GMAT Instructor; Posts: 555; Joined: Wed Oct 04, 2017 4:18 pm; Thanked: 180 times; Followed by:12 members

Jim can assemble b crates in an hour and Robert

by EconomistGMATTutor » Sun Dec 17, 2017 10:57 am

Jim can assemble b crates in an hour and Robert can assemble 2b crates in an hour. Working together at this rate, how many crates can they assemble in four hours?

A) 3b

B) 6b

C) 8b

D) 12b

E) 18b

The OA is D.

Which is the equation I should set to solve this PS question? Experts, may you give me some help, please?

Hi M7MBA,
Let's take a look at your question.

$$\text{Jim's rate }\ =\ \frac{b}{1}=b$$
$$\text{Robert's rate}\ =\ \frac{2b}{1}=2b$$
$$\text{Jim and Robert's combined rate}\ = b+2b=3b$$

Working together number of crates they assemble in 1 hour = 3b
Working together number of crates they assemble in 4 hour = 3b * 4 = 12b

Therefore, Option D is correct.

Hope it helps.
I am available if you'd like any follow up.

GMAT Prep From The Economist
We offer 70+ point score improvement money back guarantee.
Our average student improves 98 points.

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[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pm; Location: Palo Alto, CA; Thanked: 2867 times; Followed by:511 members; GMAT Score:800

by [email protected] » Sun Dec 17, 2017 1:49 pm

Hi M7MBA,

We're told that Jim can assemble B crates in an hour and Robert can assemble 2B crates in an hour. We're asked for the total number of crates that the two of them can assemble in four hours. This question can be solved Algebraically or by TESTing VALUES.

Using Algebra, you know the number of crates assembled by the two people in 1 hour (B+2B = 3B per hour). Thus, over 4 hours, you have (4)(3B) = 12B crates

TESTing VALUES, if... B = 2
Jim assembles 2 crates/hour
Robert assembles 4 crates/hour
Total = 6 crates an hour
In 4 hours.... (4)(6) = 24 crates are assembled.

Thus, we're looking for an answer that equals 24 when B=2. There's only one answer that matches.

Final Answer: D

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pm; Location: Vancouver, BC; Thanked: 5254 times; Followed by:1268 members; GMAT Score:770

by Brent@GMATPrepNow » Sun Dec 17, 2017 1:55 pm

M7MBA wrote:Jim can assemble b crates in an hour and Robert can assemble 2b crates in an hour. Working together at this rate, how many crates can they assemble in four hours?

A) 3b

B) 6b

C) 8b

D) 12b

E) 18b

We can also apply some logic to solve this question

Given: Jim can assemble b crates in 1 hour
So: Jim can assemble 2b crates in 2 hours [if we double the work time, we double the output]
So: Jim can assemble 4b crates in 4 hours [if we double the work time (again), we double the output]

Given: Robert can assemble 2b crates in 1 hour
So: Robert can assemble 4b crates in 2 hours [if we double the work time, we double the output]
So: Robert can assemble 8b crates in 4 hours [if we double the work time (again), we double the output]

So, when we COMBINE their efforts, we add their 4-hour OUTPUTS
That is, TOTAL output = color=red]4b[/color] + color=red]8b[/color] = 12b

Answer: D

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Mon Sep 16, 2019 10:20 am

M7MBA wrote:Jim can assemble b crates in an hour and Robert can assemble 2b crates in an hour. Working together at this rate, how many crates can they assemble in four hours?

A) 3b

B) 6b

C) 8b

D) 12b

E) 18b

The OA is D.

Which is the equation I should set to solve this PS question? Experts, may you give me some help, please?