During a two-week period, the price of an ounce of silver

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AAPL: Moderator; Posts: 2599; Joined: Sun Oct 29, 2017 2:08 pm; Followed by:2 members

During a two-week period, the price of an ounce of silver

by AAPL » Thu Jan 31, 2019 5:16 am

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During a two-week period, the price of an ounce of silver increased by 25 percent by the end of the first week and then decreased by 20 percent of this new price by the end of the second week. If the price of silver was x dollars per ounce at the beginning of the two-week period, what was the price, in dollars per ounce, by the end of the period?

A. 0.8x
B. 0.95x
C. x
D. 1.05x
E. 1.25x

OA C

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Source: Beat The GMAT — Problem Solving | Thu Jan 31, 2019 5:16 am

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by [email protected] » Thu Jan 31, 2019 2:07 pm

Hi All,

We're told that during a two-week period, the price of an ounce of silver INCREASED by 25 percent by the end of the first week and then DECREASED by 20 percent of this new price by the end of the second week. We're asked, if the price of silver was X dollars per ounce at the beginning of the two-week period, then what was the price, in dollars per ounce, by the end of the period. This question can be approached in a number of different ways; you might find it easiest to convert the percents to fractions and simplify the calculation all at once.

Starting value of an ounce of silver = X
After the 25% increase in price --> (5/4)(X)

The 20% decrease in price means that the value of the silver was 80% of the prior price...
After the 20% decrease of the new price --> (4/5)(5/4)(X)

The product of (4/5) and (5/4) is 20/20 = 1, so we're left with (1)(X) as the price at the end of the 2-week period.

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

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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 » Mon Feb 04, 2019 5:23 pm

AAPL wrote:GMAT Prep

During a two-week period, the price of an ounce of silver increased by 25 percent by the end of the first week and then decreased by 20 percent of this new price by the end of the second week. If the price of silver was x dollars per ounce at the beginning of the two-week period, what was the price, in dollars per ounce, by the end of the period?

A. 0.8x
B. 0.95x
C. x
D. 1.05x
E. 1.25x

Solution:

By the end of the 2-week period, the price was:

x * 1.25 * 0.8 = x

Answer: C

Scott Woodbury-Stewart
Founder and CEO
[email protected]