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The cost C of manufacturing a product can be estimated by the formula [#permalink]
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31 Jul 2011, 03:32
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The cost C of manufacturing a product can be estimated by the formula C= 0.03 rs t^2, where r ans s are amounts, in pounds, of two major ingredients and t is production time in hours. if r is increased by 50%, s increased by 20% and t decreased by 30%, by approximately what % will the estimated cost of manufacturing the product change. A. 40% increase B. 12% increase C. 4% increase D. 12% decrease E. 24% decrease
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Re: The cost C of manufacturing a product can be estimated by the formula [#permalink]
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31 Jul 2011, 05:30
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Let r=s=t=100 C = 0.03*r*s(t^2) =0.03*100*100*(100^2) =3,000,000 r1 = 50% more than r = 150 s1 = 20% more than s =120 t1 = 30% less than t = 70 C1= 0.03 * 150 *120 * 70 * 70 =0.03 * 1800 * 4900 = 54*4900 =264600 Decrease = CC1 = 3,000,000264600=35400 %Decrease = 35400/300000 * 100 = 354/30 = 11.8 ~ 12% Decrease OA D
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Re: The cost C of manufacturing a product can be estimated by the formula [#permalink]
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31 Jul 2011, 06:15
tracyyahoo wrote: The cost C of manufacturing a certain product can be estimated by the formular C=0.03rs(t^2), where r and s are the amounts, in pounds, oof the two major ingredients and t is the production time in hours. If r is increased by 50%, s is increased by 20%, and t is decreased by 30%, by approximately what percent will the estimated cost manufacturing the product change?
a) 40% increase b) 12% increase c) 4% incease d) 12% decease e) 24% decrease
pls explain me, thank you. I need it. From the formula we deduce that C directly proportional to r, s and t^2 hence an increase or decrease in these values will directly change the value of C by that factor There new r => 1.5r new s => 1.2s new t^2 = (0.7t)^2 = .49t^2 let the constant 0.03 be termed as A Putting these new values: C1 = A*1.5r*1.2s*.49t^2 C1 = 0.882A*r*s*t^2 = 0.882(C) There the net value decrease by 12% approx Hence D



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Re: The cost C of manufacturing a product can be estimated by the formula [#permalink]
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31 Jul 2011, 13:25
Hi
How did you guys determine if it was an increase or decrease?
is it because the value of c > c1?



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Re: The cost C of manufacturing a product can be estimated by the formula [#permalink]
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31 Jul 2011, 15:19
Sudhanshuacharya wrote: tracyyahoo wrote: The cost C of manufacturing a certain product can be estimated by the formular C=0.03rs(t^2), where r and s are the amounts, in pounds, oof the two major ingredients and t is the production time in hours. If r is increased by 50%, s is increased by 20%, and t is decreased by 30%, by approximately what percent will the estimated cost manufacturing the product change?
a) 40% increase b) 12% increase c) 4% incease d) 12% decease e) 24% decrease
pls explain me, thank you. I need it. From the formula we deduce that C directly proportional to r, s and t^2 hence an increase or decrease in these values will directly change the value of C by that factor There new r => 1.5r new s => 1.2s new t^2 = (0.7t)^2 = .49t^2 let the constant 0.03 be termed as A Putting these new values: C1 = A*1.5r*1.2s*.49t^2 C1 = 0.882A*r*s*t^2 = 0.882(C) There the net value decrease by 12% approx Hence D I am using the same approach as above: 50% increase = 1.5r 20% incease = 1.2s 30% decrease = .7r So new value = (1.5r)(1.2s)(.7r)^2=(15/10*12/10*49/100)(.03rst^2) Old value = (.03rst^2) Now I am approx. 49 to 50 for faster calculation  New value = (15/10*12/10*50/100) = 180/100*1/2=(90/100)(.03rst^2) New value is 90% of the old value So 10% less ....Let me see any value near 10% decreases B is the closest...So I go with B
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Re: The cost C of manufacturing a product can be estimated by the formula [#permalink]
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31 Jul 2011, 15:21
arjun007 wrote: Hi
How did you guys determine if it was an increase or decrease?
is it because the value of c > c1? Hope it is clear to you how it is decreasing ... Taking a larger value like  50 even decreased,so obviously a smaller value  49 will always decrease
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Re: The cost C of manufacturing a product can be estimated by the formula [#permalink]
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31 Jul 2011, 15:24
The reason for approximating is sometimes we make silly mistakes in calculation. So the best way is to pick smart numbers when needed.........Again it is up to you to decide the approach that works nest for you..... Some people can calculate this in head in (510) secs....then do not approximate...This is for the other folks who spend 2030 secs on multiplication(calculation)
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Re: The cost C of manufacturing a product can be estimated by the formula [#permalink]
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31 Jul 2011, 18:22
Thank you so much you guys, Why I haven't thought about using Plugin strategy. This question is very simple after I saw your explanation. Thank you again for the effot. jamifahad wrote: Let r=s=t=100
C = 0.03*r*s(t^2) =0.03*100*100*(100^2) =3,000,000
r1 = 50% more than r = 150 s1 = 20% more than s =120 t1 = 30% less than t = 70
C1= 0.03 * 150 *120 * 70 * 70 =0.03 * 1800 * 4900 = 54*4900 =264600
Decrease = CC1 = 3,000,000264600=35400 %Decrease = 35400/300000 * 100 = 354/30 = 11.8 ~ 12% Decrease
OA D



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Re: The cost C of manufacturing a product can be estimated by the formula [#permalink]
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31 Jul 2011, 19:14
tracyyahoo  Give kudos to jamifahad if you liked his approach... That is one way of saying thanks for the person spending time on your questions.....
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Re: The cost C of manufacturing a product can be estimated by the formula [#permalink]
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01 Aug 2011, 18:04
C = 0.03 r s t^2 New C = C1 = \(0.03(150/100)r(120/100)s((70/100)^2)t^2\)
=(882/1000)[0.03rst^2] as C>C1 => its a decrease
% decrease = ((original  new) /original)*100
= (118/1000) *100 ~= 12%
Answer is D.



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Re: The cost C of manufacturing a product can be estimated by [#permalink]
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Updated on: 03 May 2013, 11:19
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Initial Cost C = 0.03rs\(t^2\).
Changed Cost = \(0.03 * 1.5r * 1.2s *\) \((.7t)^2\) = \(0.03 * .882 * rs\)\(t^2\) = .882 C Change in cost = \((.882  1) * 100\) =  11.8% Negative sign indicates a decrease. So.it's a 12% decrease.
Ans : option D.  Please press +1 KUDOS if my post helps you.
Originally posted by subhendu009 on 02 May 2013, 22:22.
Last edited by subhendu009 on 03 May 2013, 11:19, edited 1 time in total.



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Re: The cost C of manufacturing a product can be estimated by [#permalink]
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02 May 2013, 22:46
[(1.5)*(1.2)*(0.7)*(0.7)  1]*100% = [1.8*0.49  1]*100% =  12%



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Re: The cost C of manufacturing a product can be estimated by [#permalink]
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02 May 2013, 23:09
lets initial values be as follows r=10, s=10, t=10 Initial cost = \(\frac{3}{100}\) X 10 X 10 X 100 Initial Cost = 300 Revised values will be r=15 > increase of 50% s=12 > increase of 20% t=7 > decrease of 30% Revised cost = \(\frac{3}{100}\) X 15 X 12 X 49 Revised cost = 265 approximatly Reduction of 35 approx reduction of 12% approx
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Re: The cost C of manufacturing a product can be estimated by [#permalink]
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05 Feb 2014, 04:35
50 % Increase = 1.5r 20 % increase = 1.2 s 30 % decrease = 0.7t > Formula says we have t² hence 0.7²
multiply: 1.5*1.2*0.7² = 0.882 = 12 % decrease. (10.882)



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Re: The cost C of manufacturing a product can be estimated by the formula [#permalink]
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24 Nov 2017, 20:52
Hi Everyone, Can someone please solve this question using the formula of successive discount (x+y+xy/100)
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