Critical Reasoning

Comets do not give off their own light but reflect light from other sources, such as the Sun. Scientists estimate the mass of comets by their brightness: the greater a comet's mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halley's comet is composed reflects 60 times less light per unit of mass than had been previously thought.

The statements above, if true, give the most support to which one of the following?

(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halley's comet is composed.
(B) Previous estimates of the mass of Halley's comet which were base on its brightness were too low.
(C) The total amount of light reflected from Halley's comet is less than scientists had previously thought.
(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.
(E) Scientists need more information before they can make a good estimate of the mass of Halley's comet.

Answer: B

I would go for D not B! See explanations:

(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halley's comet is composed.[Not supporting ]

(B) Previous estimates of the mass of Halley's comet which were base on its brightness were too low.
[At first look, it seems to be correct, but once after reading carefully "60 times less light per unit of mass than had been previously thought", it could be confirmed that we should not depend on any previous estimate which could be most probably wrong!!!, So Eliminated! ]

(C) The total amount of light reflected from Halley's comet is less than scientists had previously thought.[It's a fact not telling us why, what is the cause]

(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.[Yes, it has some resemblance with text "material of which Halley’s comet is composed", therefore reflection should be based on the material of which comet is composed, So it should be correct.]

(E) Scientists need more information before they can make a good estimate of the mass of Halley's comet.
[Not supporting ]

Hope this help.

Hi,

Can any one clarify what is the OA
if it is B then my understanding is

According to scientists,Mass is proportional to light.New Discovery indicates that the light reflected is less.So new mass should be less

B says
Previous estimates of the mass of Halley's comet which were base on its brightness were too low
which means it was less earlier and now it is having more mass which is confusing here

IMO it's B

the amount of light is same in both the cases.so cant say C

raisethebar wrote:IMO it's B

the amount of light is same in both the cases.so cant say C

Could u plz elaborate

I agree with B.

Theory: mass of size is positively correlated with the brightness of the star

Halley's mass = function of brightness

IF the brightness was underestimated, then halley's commet's mass was also underestimated.

Hope that helps.

Phirozz wrote:

raisethebar wrote:IMO it's B

the amount of light is same in both the cases.so cant say C

Could u plz elaborate

look at the option C

it says the the amount of light reflected from comet is less than scientists had previously thought. But the fact is the amout of light that comet reflect and the scientist measured is same only the calculation of mass based on the brightness of comet is wrong.

lets see mathamatically

brightness of comet =x
mass of comet =y
nw x is proportional to Y
just for example say x=y

now scientist got to know that mass is 60times less than brightness

so now new mass Y1= 60 * x

but here the amount of light(brightness) remains same.

bpgen wrote:I would go for D not B! See explanations:

(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halley's comet is composed.[Not supporting ]

(B) Previous estimates of the mass of Halley's comet which were base on its brightness were too low.
[At first look, it seems to be correct, but once after reading carefully "60 times less light per unit of mass than had been previously thought", it could be confirmed that we should not depend on any previous estimate which could be most probably wrong!!!, So Eliminated! ]

(C) The total amount of light reflected from Halley's comet is less than scientists had previously thought.[It's a fact not telling us why, what is the cause]

(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.[Yes, it has some resemblance with text "material of which Halley’s comet is composed", therefore reflection should be based on the material of which comet is composed, So it should be correct.]

(E) Scientists need more information before they can make a good estimate of the mass of Halley's comet.
[Not supporting ]

Hope this help.

It's B.

It can't be D because it is possible that scientist miscalculated mass/light relation for ALL comets, not just Halley. The statement in the passage singles out Halley, but we cannot use that to infer that the properties vary from comet to comet. All comets could still share the same properties, and the scientist errored on the calculation based on that shared property, but only discovered the error from their observation of Halley.

Hope that made sense

Comets do not give off their own light but reflect light from other sources, such as the Sun. Scientists estimate the mass of comets by their brightness: the greater a comet's mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halley's comet is composed reflects 60 times less light per unit of mass than had been previously thought.


Clearly, in light of new evidence, any previous estimates were wrong. Which is precisely what C is saying.

EDIT: I had to type B and ended up typing and highlighting C

The statements above, if true, give the most support to which one of the following?

(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halley's comet is composed.
(B) Previous estimates of the mass of Halley's comet which were base on its brightness were too low.
(C) The total amount of light reflected from Halley's comet is less than scientists had previously thought.
(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.
(E) Scientists need more information before they can make a good estimate of the mass of Halley's comet.

mohit11 wrote:Comets do not give off their own light but reflect light from other sources, such as the Sun. Scientists estimate the mass of comets by their brightness: the greater a comet's mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halley's comet is composed reflects 60 times less light per unit of mass than had been previously thought.

Mohit,

you have correctly emboldened the important parts which need to be taken into consideration.

Now look at the first emboldened part. Scientists estimate the MASS by looking at the light. They have been and are estimating mass, and not light.

In the past as well, they would have estimated the mass by looking at the light from the comet and these estimates were wrong.

Hope you now agree that B is correct!

Oh my my, B is the answer. B is what i had to type. I have no idea why i ended up typing and highlighting C.

I should not watch IPL and solve CR questions at the same time.

What is wrong with E?

reply2spg wrote:What is wrong with E?

This question is from the "MUST BE TRUE" family. Which means that we should be looking for an answer choice which we can prove from the facts given in the stimulus. As one of the experts on site once said these are "duh-answers".

(E) Scientists need more information before they can make a good estimate of the mass of Halley's comet

Here stimulus never says that Scientists need more information. For all we know in light of the new evidence, scientists might be able to accurately estimate the mass of the comet. The only answer choice which we can conclusively prove with the facts in the stimulus is B.

received a pm.

As Ron says, other posters have done a good job. Let's put some numbers to this question. First, we need to understand that the TOTAL amount of light emitted by the comet never changes.

So:

Before: 1 unit of mass--> 60 units of light. Let's say that TOTAL light is 120 units. Then, the previous estimate of the comet's mass is 120/60 = 2 units of mass.

Now: 1 unit of mass--> 1 unit of light (60 times less). The TOTAL light is still 120 units. Then, the revised estimate of the comet's mass is 120/1 = 120 units of mass.

Therefore, the previous estimate of the comet's mass (based on brightness) is too low, and choice B is correct.