Which expression is equivalent to (5x âˆ’ 3y)^2?

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AAPL: Moderator; Posts: 2636; Joined: Sun Oct 29, 2017 2:08 pmFollowed by: 2 members

by AAPL » Tue Oct 31, 2017 9:43 am

Which expression is equivalent to (5x âˆ’ 3y)^2?

$$A.\ \ 10xâˆ’6y$$
$$B.\ \ 25xâˆ’9y$$
$$C.\ \ 25x^2âˆ’9y^2$$
$$D.\ \ 25x^2âˆ’15xy+9y^2$$
$$E.\ \ 25x^2âˆ’30xy+9y^2$$

The OA is E.

Can any expert assist me with this PS question please? I need help to solve it. Thanks.

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Source: Beat The GMAT — Problem Solving | Tue Oct 31, 2017 9:43 am

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by [email protected] » Tue Oct 31, 2017 11:26 am

Hi AAPL,

At higher-and-higher score levels, the GMAT will test you on concepts that you know, but in ways that you're probably not used to thinking about.

With this question, the main concept is FOIL-ing (but you're probably not used to doing that math that anything other than individual variables; here, you're doing it with 5X and 3Y).

(5X - 3Y)^2 =
(5X - 3Y)(5X - 3Y) =
25X^2 - 15XY - 15XY + 9Y^2
25X^2 - 30XY + 9Y^2

Final Answer: E

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

Contact Rich at [email protected]

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8139; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

hi

by Scott@TargetTestPrep » Thu Nov 02, 2017 4:09 pm

AAPL wrote:Which expression is equivalent to (5x âˆ’ 3y)^2?

$$A.\ \ 10xâˆ’6y$$
$$B.\ \ 25xâˆ’9y$$
$$C.\ \ 25x^2âˆ’9y^2$$
$$D.\ \ 25x^2âˆ’15xy+9y^2$$
$$E.\ \ 25x^2âˆ’30xy+9y^2$$

Let's expand the given expression:

(5x - 3y)^2 = (5x - 3y)(5x - 3y) = 25x^2 - 30xy + 9y^2

Answer: E

Scott Woodbury-Stewart
Founder and CEO
[email protected]

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

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EconomistGMATTutor: GMAT Instructor; Posts: 555; Joined: Wed Oct 04, 2017 4:18 pmFollowed by: 12 members; Thanked: 180 times

by EconomistGMATTutor » Fri Nov 03, 2017 2:09 pm

Which expression is equivalent to (5x - 3y)^2?

$$A.\ \ 10x-6y$$
$$B.\ \ 25x-9y$$
$$C.\ \ 25x^2-9y^2$$
$$D.\ \ 25x^2-15xy+9y^2$$
$$E.\ \ 25x^2-30xy+9y^2$$

Hi AAPL,
Let's take a look at your question.

$$\left(5x-3y\right)^2$$
$$=\left(5x-3y\right)\left(5x-3y\right)$$
$$=5x\left(5x-3y\right)-3y\left(5x-3y\right)$$
$$=25x^2-15xy-\left(15xy-9y^2\right)$$
$$=25x^2-15xy-15xy+9y^2$$
$$=25x^2-30xy+9y^2$$

Therefore, Option E is correct.

Hope it helps.
I am available if you'd like any follow up.

GMAT Prep From The Economist
We offer 70+ point score improvement money back guarantee.
Our average student improves 98 points.

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8139; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Thu Oct 31, 2019 5:16 pm

AAPL wrote:Which expression is equivalent to (5x âˆ’ 3y)^2?

$$A.\ \ 10xâˆ’6y$$
$$B.\ \ 25xâˆ’9y$$
$$C.\ \ 25x^2âˆ’9y^2$$
$$D.\ \ 25x^2âˆ’15xy+9y^2$$
$$E.\ \ 25x^2âˆ’30xy+9y^2$$

The OA is E.

Can any expert assist me with this PS question please? I need help to solve it. Thanks.

Let's expand the given expression:

(5x - 3y)^2 = (5x - 3y)(5x - 3y) = 25x^2 - 30xy + 9y^2

Answer: E

Scott Woodbury-Stewart
Founder and CEO
[email protected]

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

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