Does ab= a^2 : GMAT Data Sufficiency (DS)

Does ab= a^2

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Does ab= a^2 [#permalink]

18 Dec 2012, 22:51

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Does ab = a^2

(1) a^2 = b ^2

(2) a^3 = b ^3

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Re: Does ab= a^2 [#permalink]

18 Dec 2012, 23:02

jsphcal wrote:

Does ab = a^2

(1) a^2 = b ^2

(2) a^3 = b ^3

1) a = + or - b. If a = +b. Answer is yes. If a = -b. Answer is no. Insufficient.

2)a = b. Sufficient.

Answer is B.
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Re: Does ab= a^2 [#permalink]

18 Dec 2012, 23:15

MacFauz wrote:

jsphcal wrote:

Does ab = a^2

(1) a^2 = b ^2

(2) a^3 = b ^3

1) a = + or - b. If a = +b. Answer is yes. If a = -b. Answer is no. Insufficient.

2)a = b. Sufficient.

Answer is B.

MacFauz

thanks for the reply, could you please elaborate more on the algebra use to solve?

(1) and why if a= + or -b or if a = +b stmt 1 suff, and if a = -b then insuff

did you pick numbers to test stmt 1 and 2?

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Re: Does ab= a^2 [#permalink]

18 Dec 2012, 23:27

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jsphcal wrote:

Does ab = a^2

(1) a^2 = b ^2

(2) a^3 = b ^3

ab=a^2
ab-a^2=0
a(b-a)=0

So we need a=0 or b=a

(1) doesnt help coz
a^2= b^2
a^2 is + or - a
b^2 is + or - b
We cant determine is it +ve or -ve
INSUFF

(2) helps
a^3= b^3
which means a=b or -a=-b
either way a=b
SUFF

Hence (B)
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Re: Does ab= a^2 [#permalink]

18 Dec 2012, 23:27

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jsphcal wrote:

MacFauz wrote:

jsphcal wrote:

Does ab = a^2

(1) a^2 = b ^2

(2) a^3 = b ^3

1) a = + or - b. If a = +b. Answer is yes. If a = -b. Answer is no. Insufficient.

2)a = b. Sufficient.

Answer is B.

1. We do not need to pick numbers.

1) a^2 = b^2
This means + or - a = + or - b. So we are basically given that a can be equal to b or a can be equal to -b.

If a = b, LHS of given equation becomes a^2 and hence is equal to RHS
If a = -b, LHS of given equation becomes -a^2 and hence may not be equal to RHS.

Since we are getting two different answers, this statement is insufficient.

2) a^3 = b^3
This means a = b and nothing else.

So, LHS of given equation can only be a^2 and hence is equal to RHS. Sufficient.
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Re: Does ab= a^2 [#permalink]

19 Dec 2012, 02:47

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Does ab = a^2

Does ab = a^2? --> does a(a-b)=0? does a=0 or a=b?

(1) a^2 = b ^2 --> a=b or a=-b. Not sufficient.

(2) a^3 = b ^3 --> a=b. Sufficient.

Answer: B.
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Re: Does ab= a^2 [#permalink] 19 Dec 2012, 02:47

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Does ab= a^2

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