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

number of non upgraded sensors per unit = 1/5 (U)
where U is the total number of upgraded sensors in 30 units.

=> number of non upgraded sensors in 30 units = N= 30*(1/5)U= 6U

total number of sensors = U + N = U+6U = 7U


=> upgraded is U/(7U) fraction of the total = 1/7

Answer is D.

Does anyone else find this problem hard to understand and translate into an equation? I understand it clearly after the explanation but I think it is poorly worded.

Bunuel..i got this question wrong in my MGMAT TEST.. will u send me some liink of question like this??

I got confused when i saw fraction question like this..and hard percentage question..

Thank u

Not really poorly worded, but maybe lengthy, and all those words, upgraded and non-upgraded... Annoying a little bit.

If N is the number of non-upgraded sensors in every one of the 30 units, and U is the number of those upgraded, we can write N = (1/5)*30U = 6U.
This is the key equation, it is the translation of the information " ...the number of non-upgraded sensors on one unit is 1/5 the total number of upgraded sensors on the entire satellite...".
So, we have U upgraded sensors and 6U non-upgraded ones, which means that the upgraded sensors represent U/7U = 1/7 from the total number of sensors.
No need to multiply by 30, we are given that each unit has the same number of sensors of each type. Anyway, if you multiply by 30, it will cancel out and the final ratio is the same 1/7.

Answer D.

The question needs to be read very carefully and under timed conditions it's very easy to lose track with the wording; in the review of my Mgmat exam is ranked as 700-800 level by the way, so maybe it needs to be somewhat painful

Lets say total no. of upgraded sensors on whole satellite = 30
Then each module will have 1 upgraded sensor ......... (1)
\(\frac{1}{5} th of 30 = 6\) non-upgraded sensor on each module....... (2)

Total sensors in one module = (1) + (2)

= 6+1 = 7

Total sensors on all 30 modules = 30 * 7 = 210

\(Fraction = \frac{30}{210} = \frac{1}{7}\)

Answer = D

Thanks for the explanations on this question! It took me a while to understand this question - the wording kept throwing me off. I finally approached it as below:

There are 30 Units, each with multiple sensors.

Sensors are either U or NU
Total number of sensors = total U + total NU

Given that total NU = 1/5 U; then 5NU = U
Also, there are same number of NUs in each unit; therefore 30NUs in total

Now plugging into the first equation:
Total sensors = 5NU + 30 NU = 35 NU

Question asks for total U/total sensors = 5NU/35NU = 1/7

Hope this helps!

A slightly different approach:

Let x be the number of non-upgraded sensors on a single unit (which is the same for all units). Therefore, there are 30x non upgraded units on the entire satellite.

We also know that the number of non-upgraded units on a single unit (which is x) is 1/5 the total number of upgraded sensors. Therefore, 5x equals the total number of upgraded units.

Thus, to find the fraction that have been updated, we simply take upgraded/total, which is 5x/ (30x+5x) = 5/35 = 1/7.

Answer: D

Let "n" be total number of set sensors in each unit and 'x' non- upgraded sensors.(n-x) upgraded ones.Thus,

x=1/5(n-x)(30)
Solving,
x=6/7n
There fore 1-6/7=1/7 upgraded ones

30 Units
Upgraded: U, means total #of Upgraded = 30*U
Non-Upgraded: N
\(N=0.2*30*U\) -> \(\frac{U}{N}=\frac{1}{6}\), \(\frac{U}{ALL}=\frac{1}{7}\)
Answer D

let:
x - all upgraded
y - all non-upgraded

what is x/x+y?

y/30=(1/5)x

y/30=x/5, so x=(1/6)y

(1/6)y/(1/6)y+y => (1/6)y/(7/6)y=1/7

D

let u=total upgraded sensors
let n=total non-upgraded sensors
u/5=n/30
u/n=1/6
u/(n+u)=1/7

Please advise if this is wrong:

Let, upgraded sensors be: U
Non upgraded senseors be: NU

Total= U+NU

Now., NU=(1/5)U

Hence,

Total = U+(1/5)U
= (6/5)U

U=(5/6)Total

So, wont the answer be A.

Hi,
You have gone wrong on NU = (1/5)U...
It is NU per sensor, so NU/30=(1/5)U.....NU=30/5*U=6U..

Total = U+NU= U+6U=7U..
Therefore fraction of upgraded = U/7U=1/7...

Extremely tricky wording. I hope I don't encounter something like this on my actual exam.

I really did not understand it at alBunuel please help

NUS - non upgraded sensors
US - upgraded sensors

What I am missing

Let say the total set of sensors in each unit is 5

so the total is 5*30 = 150

1/5 of the sensors that are not upgraded is 1/5 * 150 = 30

30/150 =1/5 which is not 1/7

Please, could anyone help me with this?