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Weight problem

by mnjoosub » Tue Mar 25, 2008 11:26 pm
Together, Andrea and Brian weigh p pounds; Brian weighs 10 pounds more than Andrea. Brian and Andrea's dog, Cubby, weighs p/4 pounds more than Andrea. In terms of p, What is Cubby's weight in pounds?

(A) (p/2)-10
(b) (3p/4)-5
(c) (3p/2)-5
(d) (5p/4)-10
(e) (5p)-5

The OA is B.

I can get the answer by plugging, but I would like to have the mathematical explanation.

Thanks.
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by madhavi » Wed Mar 26, 2008 6:04 am
Andrea's weight - A
Brian's weight - B
Cubby's weight -C

A+ B= p
B = A+10; A-B= -10
B+C= (p/4) + A


C=(p/4) + A-B
C=(p/4)-10

I cant find the answer in the choices. No answer clicks with plugging in either.

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by rros0770 » Wed Mar 26, 2008 7:12 am
Hey mnjoosub

What are you plugging into this equation to get answer choice B? I came across this question last week and ran into the same problem that madhavi is having. The explanation that the book gave was horrible too if I recall. I think I just dismissed the question or the explanation as incorrect. I think the problem that I had was that the wording of the question itself did not coincide with what the book was explaining and the answer it gave(could be wrong though).

Anyone else know what to do with this? Cause I'm stumped too...
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by Kaunteya1 » Wed Mar 26, 2008 7:24 am
By plugging in number one can easily solve this question

Use smart number.

Andreas weight = 35
Brians weight = 45

p = 80

Cubby's weight = 80/4 + (andreas weight) = 55lbs

now plug in p = 80 in answer choices A-E. Only B comes up with 55 pounds as cubby's weight.
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by madhavi » Wed Mar 26, 2008 7:31 am
Cubby alone is not equal to p/4 + Andrea's wt

Brian +cubby = p/4 + Andrea

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by rros0770 » Wed Mar 26, 2008 7:42 am
Yea, if I recall this now, I think the explanation given in the book followed the same logic Kaunteya1 used, in the sense that it was representing cubby's weight as:

C= p/4 + A

Pretty sure that was my problem with it. The stem says:

B + C= p/4 + A

but it appears that the answer given is for:

C= p/4 + A
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by AleksandrM » Wed Mar 26, 2008 10:05 am
Using smart numbers is fine. However, I am still interested in figuring out how to solve this one mathematically.

I have the following:

1) A + B = p 2) B = A + 10 3) B + C = p/4 + A

Then, A - B = -10 and C = p/4 + A - B

Therefore, C = p/4 + (-10) = C = p/2 - 5

If anyone has a comment about where I am going wrong on the algebra part, please.... I am more than curious.
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by madhavi » Wed Mar 26, 2008 10:09 am
The mathematical solution yields (p/4)-10

I feel something is wrong with the choices. How did you deduce p/2-5 from p/4-10??

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by its_me07 » Wed Mar 26, 2008 11:55 am
This is how i solved it.


A+ B =p
B=A+10
C=A+p/4

=>2A+10=p
A=(p-10)/2

=>c=(p-10)/2 + p/4
c=(3p-20)/4.

Hope this helps.
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by its_me07 » Wed Mar 26, 2008 11:55 am
This is how i solved it.


A+ B =p
B=A+10
C=A+p/4

=>2A+10=p
A=(p-10)/2

=>c=(p-10)/2 + p/4
c=(3p-20)/4.

Hope this helps.
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by madhavi » Wed Mar 26, 2008 12:48 pm
If C= p/4 + A, your solution works.

But does the Q say that? Isn't B+ C= A+p/4??

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by rros0770 » Wed Mar 26, 2008 1:00 pm
I have to side with Madhavi on this, I'm reading it the same way. If someone can show us where our logic is wrong that might help, but I'm pretty sure the way the question is written, we are correct.

As per the above:
Together, Andrea and Brian weigh p pounds; Brian weighs 10 pounds more than Andrea. Brian and Andrea's dog, Cubby, weighs p/4 pounds more than Andrea. In terms of p, What is Cubby's weight in pounds?

The word "AND" between Brian and Cubby implies to me that we use the sum of Brian and Cubby's weight, which is:

Brian+Cubby= p/4 + Andrea

I think it is becoming apparent that this question is supposed to tell us to use this equation :

C= p/4 + A

but the problem is that the way the question is worded it is saying the sum of Brian + Cubby is p/4 of Andrea's weight.
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by its_me07 » Wed Mar 26, 2008 2:25 pm
Its says...................Cubby weighs so the question is talking abt only Cubby's weight.


Hope this helps.
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by rajmirra » Wed Mar 26, 2008 2:35 pm
Thanks Its_me.
This question seems more like a sentence correction or perhaps critical reasoning question :D . Hey look at the subject verb agreement :roll: weighs so it should point Cubby's :idea:
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by AleksandrM » Thu Mar 27, 2008 9:11 am
The problem says that Brian AND Andrea's dog weigh..., so I don't know how it can NOT be B + C = A + p/4.

By the way, where did this problem come from... what text???????
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