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16 Oct 2017, 09:21
1
KUDOS
Expert's post
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Difficulty:

25% (medium)

Question Stats:

79% (01:10) correct 21% (01:18) wrong based on 70 sessions

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There are 4 quarts in a gallon. A gallon of motor oil sells for $12 and a quart of the same oil sells for$5. The owner of a rental agency has 6 machines and each machine needs 5 quarts of oil. What is the minimum amount of money she must spend to purchase enough oil?

(A) $84 (B)$94
(C) $96 (D)$102
(E) $150 [Reveal] Spoiler: OA _________________ Kudos [?]: 135946 [1], given: 12716 Intern Joined: 12 Oct 2017 Posts: 3 Kudos [?]: 11 [0], given: 2 Re: There are 4 quarts in a gallon. A gallon of motor oil sells for$12 [#permalink]

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16 Oct 2017, 09:39
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This post was
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6 machines need 6 x 5 = 30 quarts of oil, which equals 7 gallons and 2 quarts.
We need to calculate as many gallons all the machines need as possible since the price of 1 gallon is obviously cheaper than that of 4 quarts.

Hence, the minimum amount of money she must spend to purchase enough oil is: (7x$12) + (2x$5) = $94 Answer: B Kudos [?]: 11 [0], given: 2 Intern Joined: 10 Jun 2016 Posts: 24 Kudos [?]: 7 [0], given: 281 Re: There are 4 quarts in a gallon. A gallon of motor oil sells for$12 [#permalink]

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16 Oct 2017, 09:56
Bunuel wrote:
There are 4 quarts in a gallon. A gallon of motor oil sells for $12 and a quart of the same oil sells for$5. The owner of a rental agency has 6 machines and each machine needs 5 quarts of oil. What is the minimum amount of money she must spend to purchase enough oil?

(A) $84 (B)$94
(C) $96 (D)$102
(E) $150 4 quarts make a gallon. 1 gallon of motor oil costs$12, which means 4 quarts (in the gallon) cost $12. This implies, if bought in a gallon quantity, one quart of oil will cost$3. Therefore, to minimise the cost, the customer must maximise the quantity in gallons she buys and reduce the quantity in quarts.

6 machines with each machine consuming 5 quarts totally consume 30 quarts of oil.

To minimise the cost, the maximum quantity she could buy in gallons is 28 (largest integer less than 30 that is divisible by 4). This leaves 2 quarts to be bought individually.

Therefore, minimum cost = $(7*12) +$(2*5) = $94. Thus, B. Kudos [?]: 7 [0], given: 281 Intern Joined: 25 Apr 2017 Posts: 3 Kudos [?]: 0 [0], given: 4 There are 4 quarts in a gallon. A gallon of motor oil sells for$12 [#permalink]

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16 Oct 2017, 10:34
total oil required = 6(machines)*5(q/machine) = 30 q
since 1 gallon = 4 quarts
30 quarts = 7g+2q
7g*$12/g+2q*$5/q = 94 $ans-$94 (b)

Kudos [?]: 0 [0], given: 4

Manager
Joined: 09 Aug 2017
Posts: 59

Kudos [?]: 8 [1], given: 18

Location: United States
Concentration: Technology
GMAT 1: 640 Q44 V33
GMAT 2: 630 Q47 V29
WE: Research (Investment Banking)
Re: There are 4 quarts in a gallon. A gallon of motor oil sells for $12 [#permalink] ### Show Tags 23 Oct 2017, 07:10 1 This post received KUDOS I got B. I checked my answer multiple ways to ensure I didn’t make a silly mistake which has hampered my practice tests. I might be close to a 48 or 50 if it weren’t for the five or six problems where I do something stupid like misread a question or flip a sign. First, I read the question stem at the very end of the question. We need to figure out the minimum money this person needs to purchase enough oil. - She needs 30 quarts since 6 machines require 5 quarts each. (6*5=30) - 7 gallons will get her 28 quarts which costs$84.
- She’ll need to buy two more quarts which costs $10. 84+10=94. - I checked to see if it’d be cheaper to buy 8 gallons, but that costs 96. _________________ I'd love to hear any feedback or ways to improve my problem solving. I make a lot of silly mistakes. If you've had luck improving on stupid mistakes, I'd love to hear how you did it. Also, I appreciate any kudos. Kudos [?]: 8 [1], given: 18 VP Joined: 22 May 2016 Posts: 1137 Kudos [?]: 407 [0], given: 647 There are 4 quarts in a gallon. A gallon of motor oil sells for$12 [#permalink]

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23 Oct 2017, 14:03
Bunuel wrote:
There are 4 quarts in a gallon. A gallon of motor oil sells for $12 and a quart of the same oil sells for$5. The owner of a rental agency has 6 machines and each machine needs 5 quarts of oil. What is the minimum amount of money she must spend to purchase enough oil?

(A) $84 (B)$94
(C) $96 (D)$102
(E) $150 Approach I - Remainder I treated this as a remainder question. She needs 30 quarts of oil: 6 machines * 5 quarts ea = 30 quarts 1 gallon = 4 quarts Divide 30 by 4. Because there are 4 quarts in one gallon, the division will yield the number of gallons plus leftover quarts -- That is, the remainder will be quarts that don't "fit" and have to be bought separately. $$\frac{30}{4}$$ = 7 + R2 (quarts) (7 gallons *$12 per gallon) = $84 (2 quarts *$5 per quart) = $10$84 +10 = $94 is the minimum Answer B Approach II - Conversion, units will cancel M = machines Q = quarts G = gallons $$(6M *\frac{5Q}{1M}*\frac{1G}{4Q})= \frac{30G}{4}= 7\frac{2}{4}G$$ 7 gallons plus $$\frac{2}{4}$$ of a gallon 1 gallon=$$\frac{4}{4}$$ quarts You need 2 of those 4 quarts. Then multiply 7 gallons and 2 quarts by cost per each, and sum, as above. Minimum is$94

Kudos [?]: 407 [0], given: 647