GMAT prep: one of the four arithmetic operations

I go with C i.e., both answer taken together.

Option 1 says the sign can be either + or *.

Option 2 says the sign can be either + or -.

Thus using both, we can conclude the sign is +.

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kanha81: Master | Next Rank: 500 Posts; Posts: 431; Joined: Sat Jan 10, 2009 9:32 am; Thanked: 16 times; Followed by:1 members

Re: GMAT prep: one of the four arithmetic operations

by kanha81 » Thu Jun 04, 2009 6:53 am

Pranay wrote:I go with C i.e., both answer taken together.

Option 1 says the sign can be either + or *.

Option 2 says the sign can be either + or -.

Thus using both, we can conclude the sign is +.

Pranay,

I would say the answer would be ,simply b/c-

2 # 0 = 2
=> 2 + 0 = 2: Test the question
(5 # 6) # 2 = (5+6)+2=13
5 # (6#2) = 5 + (6+2) = 13
OR
=> 2 - 0 = 2: Test the question
(5 # 6) # 2 = (5-6)-2 = -3
5 # (6#2) = 5-(6-2) = 5-4 = 1

Hence we are able to identify the # sign stands for addition. Hence [spoiler][/spoiler]

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mbadrew: Master | Next Rank: 500 Posts; Posts: 198; Joined: Tue Feb 12, 2008 10:16 am; Location: San Francisco; Thanked: 14 times

by mbadrew » Thu Jun 04, 2009 10:18 am

D--is the right answer. All you need is one math operation to solve the problem. What you have to do is plug in the operations and see if it holds. Start with the simplest one, and that is addition. Work it out and you'll see that Each Statement Alone is Sufficient.

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kanha81: Master | Next Rank: 500 Posts; Posts: 431; Joined: Sat Jan 10, 2009 9:32 am; Thanked: 16 times; Followed by:1 members

by kanha81 » Thu Jun 04, 2009 10:24 am

mbadrew wrote:D--is the right answer. All you need is one math operation to solve the problem. What you have to do is plug in the operations and see if it holds. Start with the simplest one, and that is addition. Work it out and you'll see that Each Statement Alone is Sufficient.

mbadrew,

[D] is not the right answer, b/c-
i)
a) 5*6=6*5: (5*6) * 2 = 5 * (6*2)
b) 5+6=6+5: (5+6)+2 = 5 + (6+2)

So which operation to choose? addition or multiplication. Since more than one answer exists, this is Insufficient.

The rest of the logic follows as I posted earlier.

Hope it makes things clear.

Want to Beat GMAT.
Always do what you're afraid to do. Whoooop GMAT

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p2pg: Senior | Next Rank: 100 Posts; Posts: 35; Joined: Mon May 11, 2009 12:11 pm; Thanked: 3 times

by p2pg » Thu Jun 04, 2009 10:28 am

I think it should be A.

(1) indicates it could be addition or multiplication...
so (5*6)*2= 5*(6*2)
also (5+6)+2= 5+(6+2)
So it is TRUE in either case

(2) indicates it could be addition or subtraction
The condn will be true in case of addition and not for subtraction.

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mbadrew: Master | Next Rank: 500 Posts; Posts: 198; Joined: Tue Feb 12, 2008 10:16 am; Location: San Francisco; Thanked: 14 times

by mbadrew » Thu Jun 04, 2009 10:31 am

kanha81 wrote:
mbadrew wrote:D--is the right answer. All you need is one math operation to solve the problem. What you have to do is plug in the operations and see if it holds. Start with the simplest one, and that is addition. Work it out and you'll see that Each Statement Alone is Sufficient.
mbadrew,

[D] is not the right answer, b/c-
i)
a) 5*6=6*5: (5*6) * 2 = 5 * (6*2)
b) 5+6=6+5: (5+6)+2 = 5 + (6+2)

So which operation to choose? addition or multiplication. Since more than one answer exists, this is Insufficient.

The rest of the logic follows as I posted earlier.

Hope it makes things clear.

2 x 0 = 0, so you can't solve with multiplication. But 2 + 0 = 2

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SanjeevK: Senior | Next Rank: 100 Posts; Posts: 89; Joined: Sat May 30, 2009 2:49 am; Thanked: 9 times

by SanjeevK » Thu Jun 04, 2009 11:42 am

Let # represent the unknown operator.
A: 5#6 = 6#5. This means # can be either + or x
Let us consider that # is +
(5#6)#2 = 5 + 6 + 2 = 13
5#(6#2) = 5 + 6 + 2 = 13

Consider # is *

(5#6)#2 = 5x6x2 = 60
5#(6#2) = 5x6x2 = 60.

Hence sufficient

B: 2#0 = 0. This means # can be either + or -
Let consider that # is +
(5#6)#2 = 5 + 6 + 2 = 13
5#(6#2) = 5 + 6 + 2 = 13

Let us consider that # = -

(5#6)#2 = 5 - 6 - 2 = -3
5#(6#2) = 5 - (6 - 2) = 5 - 6 + 2 = 1

Hence insufficient

IMO A