A machine, working at a constant rate...

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swerve: Legendary Member; Posts: 2499; Joined: Sun Oct 29, 2017 2:04 pm; Followed by:6 members

A machine, working at a constant rate...

by swerve » Thu Jan 11, 2018 6:52 am

A machine, working at a constant rate, manufactures 36 straplers in 28 minutes. How many straplers does it make in 1 hr 45 min?

A. 125
B. 128
C. 135
D. 144
E. 150

The OA is C.

Please, can any expert explain this PS question for me? I tried to solve it but I can't get the correct answer. I need your help. Thanks.

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Source: Beat The GMAT — Problem Solving | Thu Jan 11, 2018 6:52 am

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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 » Thu Jan 11, 2018 7:11 am

swerve wrote:A machine, working at a constant rate, manufactures 36 straplers in 28 minutes. How many straplers does it make in 1 hr 45 min?

A. 125
B. 128
C. 135
D. 144
E. 150

We can solve this using equivalent ratios

We're comparing machine output (measured in # of staplers) with time (in minutes)

1 hr 45 min = 105 minutes
Let x = # of staplers that can be made in 105 minutes

We get: 36/28 = x/105
Cross multiply to get: (28)(x) = (36)(105)
Divide both sides by 28 to get: x = (36)(105)/(28)
To calculate this, it's useful to recognize that 105 = (7)(15) and 36 = (4)(9) and 28 = (4)(7)
So, we get: x = (4)(9)(7)(15)/(4)(7)
Simplify to get: x = (9)(15)
= 135

Answer: C

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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DavidG@VeritasPrep: Legendary Member; Posts: 2663; Joined: Wed Jan 14, 2015 8:25 am; Location: Boston, MA; Thanked: 1153 times; Followed by:128 members; GMAT Score:770

by DavidG@VeritasPrep » Thu Jan 11, 2018 10:18 am

swerve wrote:A machine, working at a constant rate, manufactures 36 straplers in 28 minutes. How many straplers does it make in 1 hr 45 min?

A. 125
B. 128
C. 135
D. 144
E. 150

The OA is C.

Please, can any expert explain this PS question for me? I tried to solve it but I can't get the correct answer. I need your help. Thanks.

We could also use our trusty R * T = W formula.

R = 36 staplers/28 minutes. 36/28 = 9/7.
T = 1 hour 45 minutes = 105 minutes
9/7 * 105 = W
9*15 = W
135 = W

The answer is C

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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 » Tue Aug 06, 2019 4:35 pm

swerve wrote:A machine, working at a constant rate, manufactures 36 straplers in 28 minutes. How many straplers does it make in 1 hr 45 min?

A. 125
B. 128
C. 135
D. 144
E. 150

The OA is C.

Please, can any expert explain this PS question for me? I tried to solve it but I can't get the correct answer. I need your help. Thanks.

We see that the machine produces 36/28 staplers per minute, so in 1 hour 45 minutes, or 105 minutes, it can produce:

36/28 x 105= 9/7 x 105 = 9 x 15 = 135 staplers

Answer: C

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