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Cant understand this math. someon eplz solve.

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by godhuli_golpo » Sun Sep 08, 2013 12:50 am
a wall with no windows 11 feet high and 20 feet long. a large roll of wallpaper costs $25 and will cover 60 square feet of wall. A small roll of wallpaper costs $6 and will cover 10 square feet of wall. What is the least cost for enough wallpaper to cover the wall?
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by vinay1983 » Sun Sep 08, 2013 1:43 am
Assuming the wall to be a rectangle, the total area is 11*20=220 sq.ft.

The larger wall paper costs $25 to cover 60 sq.ft, so it costs (220*25)/60 = approx $ 88 to cover the wall.

The smaller wall paper covers 10 sq. ft @ $6, so the area to be covered is 22 times, hence the cost will be 22*6 = $ 132.

So, I feel the least cost has to be approx $ 88.

What is the source and the OA?
You can, for example never foretell what any one man will do, but you can say with precision what an average number will be up to!
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by sanjoy18 » Sun Sep 08, 2013 2:04 am
Total sq ft= 11*20 =220 sqft
for large roll..cost per sqft= 25/60
for small roll it is 6/10
To cover up, lets consider larger roll required for x sqft wall and small roll require y sq ft wall
lest also consider Z is the cost

hence Z= (25/60)*x + (6/10)*y where x+y=220
z= [25*x+36*y]/60
for least cost we need to minimize z..
to do that we need larger value of x than the value of y (as co-efficient of x less than that of y)
hence x must be greater than 110.
now 60*z= 25*x + 36(220-x)= 36*220 -11*x
z= 132 -11*x/60
z= 132- 11*180/60
z=99
hence 99

[why i chose x=180 sqft...means 3 large roll..reason is also to minimize cost
if i had cover the 220 sqft wall using large roll it would cost 25*4=100 which greater than 99..so actually I used 3 large roll cost 25*3=75 and 4 small roll cost 4*6=24..hence total cost 75+24=99]
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by sanjoy18 » Sun Sep 08, 2013 2:15 am
vinay1983 wrote:Assuming the wall to be a rectangle, the total area is 11*20=220 sq.ft.

The larger wall paper costs $25 to cover 60 sq.ft, so it costs (220*25)/60 = approx $ 88 to cover the wall.

The smaller wall paper covers 10 sq. ft @ $6, so the area to be covered is 22 times, hence the cost will be 22*6 = $ 132.

So, I feel the least cost has to be approx $ 88.

What is the source and the OA?
Vinay1983..

it is not $88..it actually cost $100. as when you covered 220 sqft wall using large roll..You are actually using 4 large roll.So cost will be 25*4=$100..But actual answer would be $99 ..see my post .
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by ikaplan » Sun Sep 08, 2013 4:42 am
You should assume that you can not split a large roll into smaller pieces. In order to cover the total wall area is 220 sq. ft you need 3 large rolls and 4 small rolls.

3* $25= $75
4* $6= $24

total $99
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by vinay1983 » Sun Sep 08, 2013 9:37 am
sanjoy18 wrote:
vinay1983 wrote:Assuming the wall to be a rectangle, the total area is 11*20=220 sq.ft.

The larger wall paper costs $25 to cover 60 sq.ft, so it costs (220*25)/60 = approx $ 88 to cover the wall.

The smaller wall paper covers 10 sq. ft @ $6, so the area to be covered is 22 times, hence the cost will be 22*6 = $ 132.

So, I feel the least cost has to be approx $ 88.

What is the source and the OA?
Vinay1983..

it is not $88..it actually cost $100. as when you covered 220 sqft wall using large roll..You are actually using 4 large roll.So cost will be 25*4=$100..But actual answer would be $99 ..see my post .
Yep I realised it late enough.It necessarily has to be a combi of paper rolls, only then can we acheive the desired outcome.
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by Java_85 » Sun Sep 08, 2013 11:46 am
IMO 99$ it is.
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by [email protected] » Sun Sep 08, 2013 1:19 pm
Hi godhuli_golpo,

This question doesn't have the "style" or wording of a GMAT question. What is the source? In addition, you would have 5 answers to work with, which could help you to catch or avoid a math mistake and/or help you to estimate the correct answer. Can you include those answer choices?

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by godhuli_golpo » Wed Sep 11, 2013 8:41 pm
To all,
I got this math from a bank job test. correct answer is given $99.
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by ganeshrkamath » Thu Sep 12, 2013 12:01 am
godhuli_golpo wrote:a wall with no windows 11 feet high and 20 feet long. a large roll of wallpaper costs $25 and will cover 60 square feet of wall. A small roll of wallpaper costs $6 and will cover 10 square feet of wall. What is the least cost for enough wallpaper to cover the wall?
$25 for 60 square feet of wall, $6 for 10 square feet of wall.

We have to divide the given area into 60 sq.ft. and 10 sq.ft.

Total area = 11*20 = 220
220 = 3*60 + 4*10

Cost = 3*25 + 4*6 = 75 + 24
= [spoiler]$99[/spoiler]

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