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The symbol ⊙ represents one of the operations: addition, subtraction,

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Math Revolution GMAT Instructor
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The symbol ⊙ represents one of the operations: addition, subtraction, [#permalink]

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New post 09 Jan 2018, 03:52
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[GMAT math practice question]

The symbol ⊙ represents one of the operations: addition, subtraction, multiplication, and division. Is 2⊙2=4?

1) 1⊙1=1
2) (-1) ⊙ (-1)=0

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Re: The symbol ⊙ represents one of the operations: addition, subtraction, [#permalink]

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New post 09 Jan 2018, 04:33
MathRevolution wrote:
[GMAT math practice question]

The symbol ⊙ represents one of the operations: addition, subtraction, multiplication, and division. Is 2⊙2=4?

1) 1⊙1=1
2) (-1) ⊙ (-1)=0


As we have only 4 options, we'll just list them all.
This is an Alternative approach.

(1) Since
1*1 = 1
1/1 =1
1 + 1 = 2
1-1 =0
then ⊙ can be * or / and 2⊙2 is 4 or 1.
Insufficient!

(2) Since
-1 * -1 = 1
-1 / -1 =1
-1 + -1 = -2
-1 - -1 =0
Then ⊙ must be - and 2⊙2=0
Sufficient to answer NO.

(B) is our answer.
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Expert Post
Math Revolution GMAT Instructor
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Joined: 16 Aug 2015
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Re: The symbol ⊙ represents one of the operations: addition, subtraction, [#permalink]

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New post 11 Jan 2018, 01:39
=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.
The first step of the VA (Variable Approach) method is to modify the original condition and the question, and then recheck the question.
Since only 2 + 2 = 4 and 2 * 2 = 4, the question asks if ⊙ is addition or multiplication.
Condition 1)
Since 1 * 1 = 1 and 1 / 1 = 1, ⊙ is multiplication or division.
Condition 1) is not sufficient.
Condition 2)
Since (-1) – (-1) = 0, ⊙ is subtraction. The answer is “no”.
CMT1 states that “no” is also an answer.
Condition 2) is sufficient.

Therefore, the answer is B.
Answer: B
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Re: The symbol ⊙ represents one of the operations: addition, subtraction, [#permalink]

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New post 11 Jan 2018, 02:12
New to this topic and really thanks for sharing this useful ideas.
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Re: The symbol ⊙ represents one of the operations: addition, subtraction,   [#permalink] 11 Jan 2018, 02:12
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