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# A satellite is composed of 30 modular units, each of which

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Joined: 03 Aug 2017
Posts: 102
Re: A satellite is composed of 30 modular units, each of which  [#permalink]

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23 Aug 2018, 03:50
varunmaheshwari wrote:
A satellite is composed of 30 modular units, each of which is equipped with a set of sensors, some of which have been upgraded. Each unit contains the same number of non-upgraded sensors. If the number of non-upgraded sensors on one unit is 1/5 the total number of upgraded sensors on the entire satellite, what fraction of the sensors on the satellite have been upgraded?

A. 5/6
B. 1/5
C. 1/6
D. 1/7
E. 1/24

This is how i solved
Let the total no of upgraded sensor in entire sat be 30 ( ie 1 per 30 modular units )
now total no of unupgraded sensor per uinit = 1/5* 30 = 6
Total no of not upgraded sensore = 6* 30 = 180
Total no of sensors = 180 + 30 = 210

Target quest
= total no of upgraded sensors / total no of sesors

= 30 / 210 = 1/7
=D
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Joined: 01 Feb 2018
Posts: 4
GMAT 1: 640 Q48 V30
Re: A satellite is composed of 30 modular units, each of which  [#permalink]

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18 Mar 2019, 07:15
Let total number of non-upgraded sensors be y
And total number of upgraded sensors be x
y/30 = x/5
>> y/x = 6/1
>> x/(x+y) = 1/(1+6) = 1/7
Hence, Option D

Please give a kudos if you like this solution
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Posts: 4355
Re: A satellite is composed of 30 modular units, each of which  [#permalink]

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28 Aug 2019, 08:47
Top Contributor
varunmaheshwari wrote:
A satellite is composed of 30 modular units, each of which is equipped with a set of sensors, some of which have been upgraded. Each unit contains the same number of non-upgraded sensors. If the number of non-upgraded sensors on one unit is 1/5 the total number of upgraded sensors on the entire satellite, what fraction of the sensors on the satellite have been upgraded?

A. 5/6
B. 1/5
C. 1/6
D. 1/7
E. 1/24

A student asked me to add some graphics to my solution, so......

A satellite is composed of 30 modular units, each of which is equipped with a set of sensors, some of which have been upgraded. Each unit contains the same number of non-upgraded sensors.
So, here's a sketch of 30 modular units.

The circles inside each unit represent sensors. The circles with black centers represent NON-upgraded sensors, and the empty red circles represent upgraded sensors.
For my sketch, I placed ONE NON-upgraded sensor in each of the 30 modular units (since we're told that each unit contains the same number of non-upgraded sensors)

The number of non-upgraded sensors on ONE UNIT is 1/5 the total number of upgraded sensors on the ENTIRE satellite
This tells us that there aren't many upgraded sensors among the satellite's 30 modular units
So, let's REDRAW the diagram to start with 1 NON-upgraded sensor in each of the 30 modular units

Okay, so if there's 1 NON-upgraded sensor in EACH of the 30 modular units, then there is a TOTAL of 5 UPgraded sensors on the ENTIRE satellite.

At this point, our diagram meets all of the conditions in the question.

What fraction of the sensors on the satellite have been upgraded?
We can see that we have a total of 35 sensors, and 5 of them are upgraded.
So, the fraction = 5/35 = 1/7

Cheers,
Brent
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Re: A satellite is composed of 30 modular units, each of which  [#permalink]

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30 Aug 2019, 05:19
jagdeepsingh1983 wrote:
A satellite is composed of 30 modular units, each of which is equipped with a set of sensors, some of which have been upgraded. Each unit contains the same number of non-upgraded sensors. If the number of non-upgraded sensors on one unit is 1/5 the total number of upgraded sensors on the entire satellite, what fraction of the sensors on the satellite have been upgraded?

No of Units-30
Let there T-Total no of sensor
U-no of upgraded sensors in one unit
Nu-No of Not upgraded senor in one unit

T= 30U+30Nu

Now we know that Nu=1/5 (30U)= 6U

So Total= 30U+30*6U = 30U+180U= 210U

Fraction= 30U/210U = 1/7 Answer is D

Regards
Jagdeep
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Hello jagdeep,
Thank you very much for your explanation, you turn a difficult exercise in a easy one.
But I have one question:

If you say T= 30U+30Nu, don't you assume each U is equal to all Us such as Nu is equal to all Nus? - N1=N2=N3=...=N30
I mean, every N is equal (and Nu) and the question didn't say it. Because I didn't get it, I couldn't solve the exercise.

Thank you!
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Yasmin C G Teixeira
Re: A satellite is composed of 30 modular units, each of which   [#permalink] 30 Aug 2019, 05:19

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