If a certain wheel turns at a constant rate of x revolutions

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BTGmoderatorLU: Moderator; Posts: 2544; Joined: Sun Oct 15, 2017 1:50 pmFollowed by: 6 members

by BTGmoderatorLU » Sat Oct 27, 2018 2:17 pm

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Source: GMAT Prep

If a certain wheel turns at a constant rate of x revolutions per minute, how many revolutions will the wheel make in k seconds?

A. 60kx
B. kx
C. x/k
D. x/60k
E. kx/60

The OA is E.

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Source: Beat The GMAT — Problem Solving | Sat Oct 27, 2018 2:17 pm

fskilnik@GMATH: GMAT Instructor; Posts: 1449; Joined: Sat Oct 09, 2010 2:16 pmFollowed by: 33 members; Thanked: 59 times

by fskilnik@GMATH » Sat Oct 27, 2018 6:46 pm

BTGmoderatorLU wrote:Source: GMAT Prep

If a certain wheel turns at a constant rate of x revolutions per minute, how many revolutions will the wheel make in k seconds?

A. 60kx
B. kx
C. x/k
D. x/60k
E. kx/60

$$x\,\,{\rm{revol}}\,\,\, \leftrightarrow \,\,\,1\,\,\min $$
$$?\,\,=\,\,\# \,\,{\rm{revol}}\,\,{\rm{in}}\,\,k\,\,\sec $$
Trivial application of UNITS CONTROL, one of the most powerful tools of our method!
$$? = k\,\,\sec \,\,\left( {{{1\,\,\min } \over {60\,\,\sec }}} \right)\,\,\left( {{{x\,\,{\rm{revol}}} \over {1\,\,\min }}} \right) = \,\,\,{{kx} \over {60}}\,\,\,\,\left[ {{\rm{revol}}} \right]$$

This solution follows the notations and rationale taught in the GMATH method.

Regards,
Fabio.

Fabio Skilnik :: GMATH method creator ( Math for the GMAT)
English-speakers :: https://www.gmath.net
Portuguese-speakers :: https://www.gmath.com.br

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

by [email protected] » Sun Oct 28, 2018 7:18 pm

Hi All,

We're told that a certain wheel turns at a constant rate of X revolutions per MINUTE. We're asked for the number of revolutions that the wheel will make in K SECONDS. This question can be solved in a number of different ways, including by TESTing VALUES.

IF.... X=2 and K=60...
The wheel makes 2 revolutions per MINUTE and in 60 SECONDS it makes 2 revolutions.
Thus, we're looking for an answer that equals 2 when we TEST X=2 and K=60 into the answer. There's only one answer that matches...

Final Answer: E

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

Contact Rich at [email protected]

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8135; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Tue Oct 30, 2018 6:12 pm

BTGmoderatorLU wrote:Source: GMAT Prep

If a certain wheel turns at a constant rate of x revolutions per minute, how many revolutions will the wheel make in k seconds?

A. 60kx
B. kx
C. x/k
D. x/60k
E. kx/60

Since k seconds is k/60 minutes, the wheel will make x * k/60 = xk/60 revolutions in k seconds.

Alternate Solution:

We can create a proportion: "x revolutions is to 60 seconds as q revolutions is to k seconds," and our goal is to solve for q:

x/60 = q/k

xk = 60q

xk/60 = q

Answer: E

Scott Woodbury-Stewart
Founder and CEO
[email protected]

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

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