Over a three-week period, the price of an ounce of gold

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swerve: Legendary Member; Posts: 2568; Joined: Sun Oct 29, 2017 2:04 pmFollowed by: 6 members

by swerve » Tue Apr 10, 2018 8:37 am

Over a three-week period, the price of an ounce of gold increased by 25% in the first week, decreased by 20% in the following week, and increased by 5% in the third week. If the price of gold was G dollars per ounce at the beginning of the three weeks, what was the price, in terms of G, at the end of the three weeks?

A. 0.95G
B. G
C. 1.05G
D. 1.1G
E. 1.15G

The OA is C.

Please, can anyone explain this PS question for me? I tried to solve it but I can't get the correct answer. I need your help. Thanks.

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Source: Beat The GMAT — Problem Solving | Tue Apr 10, 2018 8:37 am

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gold price

by GMATGuruNY » Tue Apr 10, 2018 9:01 am

swerve wrote:Over a three-week period, the price of an ounce of gold increased by 25% in the first week, decreased by 20% in the following week, and increased by 5% in the third week. If the price of gold was G dollars per ounce at the beginning of the three weeks, what was the price, in terms of G, at the end of the three weeks?

A. 0.95G
B. G
C. 1.05G
D. 1.1G
E. 1.15G

Let G = 100.
After a 25% increase, the price = 100 + (25/100)(100) = 100 + 25 = 125.
After a 20% decrease, the price = 125 - (20/100)(125) = 125 - 25 = 100.
After a 5% increase, the price = 100 + (5/100)(100) = 100 + 5 = 105.

The question stem asks for the final price: 105.
Now plug G=100 into the answer choices to see which yields a final price of $105.
Only C works:
(1.05)G = (1.05)(100) = 105.

The correct answer is C.

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8188; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Mon Apr 16, 2018 3:42 pm

swerve wrote:Over a three-week period, the price of an ounce of gold increased by 25% in the first week, decreased by 20% in the following week, and increased by 5% in the third week. If the price of gold was G dollars per ounce at the beginning of the three weeks, what was the price, in terms of G, at the end of the three weeks?

A. 0.95G
B. G
C. 1.05G
D. 1.1G
E. 1.15G

The price of gold at the end of the 3 weeks was:

G x 1.25 x 0.8 x 1.05 = 1.05G = 1.05G

Answer: C

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