Dear
BrentGMATPrepNow, @Care
In my view, the difficult degree is not the math, but it is the English. For not native people such as me, I did not understand the meaning of the first sentence: "A satellite is composed of 30 modular units, each of which is equipped with a set of sensors, some of which have been upgraded".
Now, when my English grammar was upgraded a bit, I understood it as follows:
A satellite is composed of 30 modular units,
each of which is equipped with a set of sensors
= each of modular unit is equipped with a set of sensors.some of which have been upgraded =
in each of modular unit, some of sensors have been upgrade (saying U), and the rest, of course, are non-upgraded sensors (saying Un).
Now, the total of sensors of 30 units is: 30*(U+Un).
the number of non-upgraded sensors on one unit is Un.
the total number of upgraded sensors on the entire satellite: 30*U.
Un = 1/5 (30*U) = 6*U
The fraction of the sensors on the satellite have been upgraded: 30U / 30 *( U + 6U) = 1/7
In fact, in official math books in my country, authors avoid this wording style as it confuses readers.
Anyway, it is English, we have to accept.
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. 1/24BrentGMATPrepNow wrote:
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 satelliteThis 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.
So, let's add
5 UPgraded sensors to our diagram to get:
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
Answer: D
Cheers,
Brent
Cares wrote:
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.