BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

calorie trouble

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Junior | Next Rank: 30 Posts
Posts: 12
Joined: Wed Nov 18, 2009 9:55 am

calorie trouble

by MG368 » Tue Dec 01, 2009 8:42 am
A breakfast that consists of 1 ounce of corn puffs and 8 ounces of fruit X provides 257 calories. When 8 ounces of fruit Y is substituted for the 8 ounces of fruit X, the total number of calories is reduced to 185. If fruit X provides 1.8 times as many calories as fruit Y, how many calories does 8 ounces of fruit Y alone provide ?
(A) 11.25
(B) 72
(C) 90
(D) 95
(E) 129.6

OA is C
Top
Source: — Problem Solving |
Legendary Member
Posts: 869
Joined: Wed Aug 26, 2009 3:49 pm
Location: California
Thanked: 13 times
Followed by:3 members

by heshamelaziry » Tue Dec 01, 2009 10:00 am
I don't understan how OA is C ?

1C + 8(1.8y) = 257

1C + 8y = 185

Subtracting 2 from 1 we get y = 11.25 (A)
Top
Master | Next Rank: 500 Posts
Posts: 177
Joined: Thu Aug 14, 2008 11:59 am
Thanked: 25 times

by mp2437 » Tue Dec 01, 2009 10:25 am
when you replace fruit x with fruit y, you go from 257 calories to 185, or a difference of 72. That means X - Y = 72. You could think about this way: you know that with fruit X you have 257 calories, but when you take it away (subtract X) and add fruit Y (add Y), then you have 72 calories less:

-X + Y = -72, rearranging you get X - Y = 72.

You also know that X = 1.8Y, so plug it in:

X - Y = 72
1.8Y - Y = 72
0.8Y = 72
Y = 90

Choice C.
Top
Legendary Member
Posts: 869
Joined: Wed Aug 26, 2009 3:49 pm
Location: California
Thanked: 13 times
Followed by:3 members

by heshamelaziry » Tue Dec 01, 2009 10:38 am
mp2437 wrote:when you replace fruit x with fruit y, you go from 257 calories to 185, or a difference of 72. That means X - Y = 72. You could think about this way: you know that with fruit X you have 257 calories, but when you take it away (subtract X) and add fruit Y (add Y), then you have 72 calories less:

-X + Y = -72, rearranging you get X - Y = 72.

You also know that X = 1.8Y, so plug it in:

X - Y = 72
1.8Y - Y = 72
0.8Y = 72
Y = 90

Choice C.
I can't comprehend your solution, although I understand it. In the test i will do what I just did, because I don't understand the difference between the two ways.
Top
Senior | Next Rank: 100 Posts
Posts: 84
Joined: Sat Oct 03, 2009 1:13 pm
Thanked: 11 times

by djkvakin » Tue Dec 01, 2009 12:08 pm
heshamelaziry wrote:
mp2437 wrote:when you replace fruit x with fruit y, you go from 257 calories to 185, or a difference of 72. That means X - Y = 72. You could think about this way: you know that with fruit X you have 257 calories, but when you take it away (subtract X) and add fruit Y (add Y), then you have 72 calories less:

-X + Y = -72, rearranging you get X - Y = 72.

You also know that X = 1.8Y, so plug it in:

X - Y = 72
1.8Y - Y = 72
0.8Y = 72
Y = 90

Choice C.
I can't comprehend your solution, although I understand it. In the test i will do what I just did, because I don't understand the difference between the two ways.
You are solving for y. which turns out to be 11.25/ The problem asks you to answer how many calories there are in 8 oz of y. which would be 8*y. In this case 11.25*8=90. So both solutions are applicable. One is just faster than another.
Top
Master | Next Rank: 500 Posts
Posts: 156
Joined: Sat Jul 19, 2008 6:41 am
Thanked: 8 times

by enniguy » Thu Dec 03, 2009 11:21 am
Firstly, The question is wrongly typed. Also, MG368, please use Spoilers like this for OA. [spoiler]OA:C[/spoiler]. Corrected question below.
MG368 wrote:A breakfast that consists of 1 ounce of corn puffs and 8 ounces of fruit X provides 257 calories. When 8 ounces of fruit X is substituted for the 8 ounces of fruit Y, the total number of calories is reduced to 185. If fruit X provides 1.8 times as many calories as fruit Y, how many calories does 8 ounces of fruit Y alone provide ?
(A) 11.25
(B) 72
(C) 90
(D) 95
(E) 129.6

OA is C
From the question these are the equations:
p + 8x = 257 -- (1)
p + 8y = 185 -- (2)
x = 1.8 y. -- (3)

What's the question? Find 8y. (Not y)
Replace equation 3 in equation 1 and subtract equation 1 - equation 2.
You will get,
8(1.8y) - 8y = 72.
=> 8y (1.8 - 1) = 72
=> 8y = 72/0.8
=> 8y = 90.
Which is the answer.
Top
User avatar
GMAT Instructor
Posts: 3225
Joined: Tue Jan 08, 2008 2:40 pm
Location: Toronto
Thanked: 1710 times
Followed by:614 members
GMAT Score:800

by Stuart@KaplanGMAT » Thu Dec 03, 2009 4:07 pm
heshamelaziry wrote:I don't understan how OA is C ?

1C + 8(1.8y) = 257

1C + 8y = 185

Subtracting 2 from 1 we get y = 11.25 (A)
As pointed out in another post, your mistake is that you didn't read the question carefully enough - up until that point your math was great.

You let y = the number of calories in 1 ounce of fruit y. Since the question asks for the number of calories in 8 ounces of y, you need to multiply your result by 8.

It's not even slightly surprising that your calculated result was among the choices. One of the most common traps on the GMAT is to provide answer choices that are interim calculations in arriving at the final solution, especially on more complex questions.

Here are some examples:

Question asks: how long does it take x and y to paint 2 rooms?
Trap answer: how long it takes them to paint 1 room.

Question asks: how much money does Bob have left?
Trap answer: how much money Bob spent.

Question asks: what's the revenue from the sale of 2 donuts and 3 cups of coffee?
Trap answer: revenue from the sale of 1 donut.
Trap answer: revenue from the sale of 1 cup of coffee.
Trap answer: revenue from the sale of 2 donuts.
Trap answer: revenue from the sale of 3 cups of coffee.

So, what's the key to happiness? It's:

Step 4 of the Kaplan Method for PS: after doing all your calculations, always double check the question.
Image

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course
Top
Post new topic Post Reply
• Page 1 of 1