Oil, vinegar, and water are mixed in a 3 to 2 to 1 ratio to

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BTGmoderatorLU: Moderator; Posts: 2505; Joined: Sun Oct 15, 2017 1:50 pm; Followed by:6 members

Oil, vinegar, and water are mixed in a 3 to 2 to 1 ratio to

by BTGmoderatorLU » Sat Dec 08, 2018 5:07 am

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Source: Manhattan Prep

Oil, vinegar, and water are mixed in a 3 to 2 to 1 ratio to make salad dressing. If Larry has 8 cups of oil, 7 cups of vinegar, and access to any amount of water, what is the maximum number of cups of salad dressing he can make with the ingredients he has available, if fractional cup measurements are possible?

A. 12
B. 13
C. 14
D. 15
E. 16

The OA is E.

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Source: Beat The GMAT — Problem Solving | Sat Dec 08, 2018 5:07 am

fskilnik@GMATH: GMAT Instructor; Posts: 1449; Joined: Sat Oct 09, 2010 2:16 pm; Thanked: 59 times; Followed by:33 members

by fskilnik@GMATH » Sat Dec 08, 2018 4:53 pm

BTGmoderatorLU wrote:Source: Manhattan Prep

Oil, vinegar, and water are mixed in a 3 to 2 to 1 ratio to make salad dressing. If Larry has 8 cups of oil, 7 cups of vinegar, and access to any amount of water, what is the maximum number of cups of salad dressing he can make with the ingredients he has available, if fractional cup measurements are possible?

A. 12
B. 13
C. 14
D. 15
E. 16

Excellent opportunity for the k technique!
$$\left\{ \matrix{
\,{\rm{oil}} = 3k\,\,\,\,\,\, \to \,\,\,\,\,\,3k \le 8\,\,\, \Rightarrow \,\,\,k \le 2{2 \over 3} \hfill \cr
\,{\rm{vin}} = 2k\,\,\,\,\,\, \to \,\,\,\,\,\,2k \le 7\,\,\, \Rightarrow \,\,\,k \le 3{1 \over 2} \hfill \cr
\,{\rm{wat}} = k \hfill \cr} \right.$$
$$?\,\,:\,\,\left( {3k + 2k + k} \right)\,\,{\rm{where}}\,\,k = 2{2 \over 3}\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,? = 6\left( {2 + {2 \over 3}} \right) = 12 + 4 = 16$$

This solution follows the notations and rationale taught in the GMATH method.

Regards,
Fabio.

Fabio Skilnik :: GMATH method creator ( Math for the GMAT)
English-speakers :: https://www.gmath.net
Portuguese-speakers :: https://www.gmath.com.br

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GMAT/MBA Expert

Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pm; Location: Vancouver, BC; Thanked: 5254 times; Followed by:1268 members; GMAT Score:770

by Brent@GMATPrepNow » Mon Dec 10, 2018 9:56 am

BTGmoderatorLU wrote:Oil, vinegar, and water are mixed in a 3 to 2 to 1 ratio to make salad dressing. If Larry has 8 cups of oil, 7 cups of vinegar, and access to any amount of water, what is the maximum number of cups of salad dressing he can make with the ingredients he has available, if fractional cup measurements are possible?

A. 12
B. 13
C. 14
D. 15
E. 16

GIVEN: oil: vinegar : water = 3 : 2 : 1

Let's first try to use ALL 8 cups of oil
Take 3 : 2 : 1 and multiply all 3 parts by 8/3 to get the EQUIVALENT ratio 8 : 16/3 : 8/3
Simplify to get: 8 : 5 1/3 : 2 2/3
So, in this case, the dressing is comprised of 8 cups of oil, 5 1/3 cups of vinegar, and 2 2/3 cups of water
Notice that we have enough vinegar to make this batch.

8 cups + 5 1/3 cups + 2 2/3 cups = 16 cups
So, the TOTAL volume = 16 cups

IMPORTANT: Notice that 16 is the biggest answer choice.
This means we need not explore what happens when we try to use ALL 7 cups on the vinegar, since the answer choices tell us that we will NOT get a value greater than 16

Answer: E

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Fri Mar 15, 2019 5:37 pm

BTGmoderatorLU wrote:Source: Manhattan Prep

Oil, vinegar, and water are mixed in a 3 to 2 to 1 ratio to make salad dressing. If Larry has 8 cups of oil, 7 cups of vinegar, and access to any amount of water, what is the maximum number of cups of salad dressing he can make with the ingredients he has available, if fractional cup measurements are possible?

A. 12
B. 13
C. 14
D. 15
E. 16

The OA is E.

We can create the ratio of oil : vinegar : water = 3x : 2x : x

Since Larry has 8 cups of oil, we have:

3x = 8

x = 8/3 = 2 â…”

Since Larry has 7 cups of vinegar, we have:

2x = 7

x = 7/2 = 3.5

We see that we must use the smaller of the two values of x since, if we used 3.5 for x, we would need to have 3 x 3.5 = 10.5 cups of oil (but we have only 8 cups of oil).

Since the total number of cups of dressing is 3x + 2x + x = 6x and x = 8/3, the total number of cups of dressing that can be made is 8/3 x 6 = 16 cups.

Answer: E

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