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If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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28 Apr 2019, 18:34
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If \(a = 4\), what is the value of \(c\)? (1) \((abc)^4 = (ab^2c^3)^2\) (2) \(b = 5\)
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If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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Updated on: 01 May 2019, 01:46
SajjadAhmad wrote: If \(a = 4\), what is the value of \(c\)?
(1) \((abc)^4 = (ab^2c^3)^2\)
(2) \(b = 5\) solve for #1 \((abc)^4 = (ab^2c^3)^2\) we get a^2=c^2 c = +/4 insufficeint #2 only b given c relation missing from 1 & 2 we cannot get any info IMO E
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Originally posted by Archit3110 on 29 Apr 2019, 07:59.
Last edited by Archit3110 on 01 May 2019, 01:46, edited 1 time in total.



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Re: If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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29 Apr 2019, 09:38
i think answer is E, a2=c2 does not mean a=c, it means c2=16, now c can be +4 and 4, so not enough to give exact value of c, hence E is answer



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Re: If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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29 Apr 2019, 09:41
lifeforhuskar wrote: i think answer is E, a2=c2 does not mean a=c, it means c2=16, now c can be +4 and 4, so not enough to give exact value of c, hence E is answer lifeforhuskareven i thoight that E., but if you square after a^2=c^2 ; you shall get a=c
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Re: If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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29 Apr 2019, 09:45
a = 4 is given , so c can not be 4 , it will take only +4 .
hope this helps
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Re: If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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29 Apr 2019, 09:46
Archit3110 wrote: lifeforhuskar wrote: i think answer is E, a2=c2 does not mean a=c, it means c2=16, now c can be +4 and 4, so not enough to give exact value of c, hence E is answer lifeforhuskareven i thoight that E., but if you square after a^2=c^2 ; you shall get a=c I dont agree, you can try and put 4 or +4 in the equation, both are giving same results. May be we need ER on this.



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Re: If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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29 Apr 2019, 09:53
solve for #1 (abc)4=(ab2c3)2(abc)4=(ab2c3)2 we get a^2=c^2
c= √a² c= √16 c= +/ 4
Hence E But gmat considers Roots to be +ve and square to have both +/ sign Hence A.
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Re: If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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29 Apr 2019, 10:05
[quote="mohitranjan05"]solve for #1 (abc)4=(ab2c3)2(abc)4=(ab2c3)2 we get a^2=c^2
c= √a² c= √16 c= +/ 4
But gmat considers Roots to be +ve and square to have both +/ sign
Can someone explain this...thanks



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Re: If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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29 Apr 2019, 10:40
The Answer is (E)
Given A=4, c=?
1) (abc)^4= (ab^2c^3)^2 a^4b^4c^4  a^2b^4c^6 = 0 a^2b^4c^2(a^2  c^2) = 0 This implies that either of a,b,c take a zero value or a^2=c^2. Since we know that a=4, but if b=0, then c can take any value. Hence N.S
2) b=5 NS on its own
Combining both we get either c=0 or c^2=a^2 which means c can have two possible values c=0 and c=a=4. Hence NS
Answer (E)



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If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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29 Apr 2019, 10:56
Also, in this problem when a^2=c^2, this means that a = c and since its already given that a=4, we do not need to consider the ve case.



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Re: If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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29 Apr 2019, 12:21
SajjadAhmad wrote: If \(a = 4\), what is the value of \(c\)?
(1) \((abc)^4 = (ab^2c^3)^2\)
(2) \(b = 5\) by (1) we get a^4b^4c^4a^2b^4c^6=0 and a^2b^4c^4(a^2c^2) = 0 and a^2b^4c^4(a+c)(ac) = 0. Since we can factor out (a+c)(ac) = 0 we see that a=+c, thus c=+4 are two solutions. Since we get AT LEAST 2 solutions for C we can mark NS (2) b =5? So what. Nothing related to c NS (1) and (2)  Copy from (1), and plug in b = 5 > a^2(5)^4(4+c)(4c) = 0. Even after plugging in b = 5 we still get at least two solutions for c thus NS E



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If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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29 Apr 2019, 12:23
m1033512 wrote: a = 4 is given , so c can not be 4 , it will take only +4 .
hope this helps
Posted from my mobile device I don't quite get, how you reached to this conclusion that c can not be 4. Can you explain this a bit further? IMO, St(1) does not provide us with any of the values, but a = 4. We know nothing about b and c. So, b and c can have ANY of the THREE signs : Positive, Negative, and Zero. B and C can have a range of values. If b = 0 then C can have any value on the number line and vice versa. Not Sufficient. St(2) is clearly insufficient. St(1) + St(2) : After combining both the statements, we sill get C^2 = 16 and thus, C can be +4 or 4. Two values. Not Sufficient. The problem is with the square, we don't know whether it is +4 or  4, but if we had something like c^odd number = Some positive number, then surely C would have been a positive number. I hope this helps. I don't mind Kudos!



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Re: If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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29 Apr 2019, 13:15
a=c so two cases c=a or c=a Archit3110 wrote: SajjadAhmad wrote: If \(a = 4\), what is the value of \(c\)?
(1) \((abc)^4 = (ab^2c^3)^2\)
(2) \(b = 5\) solve for #1 \((abc)^4 = (ab^2c^3)^2\) we get a^2=c^2 square both sides a=c sufficeint #2 only b given c relation missing IMO A Posted from my mobile device



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Re: If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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29 Apr 2019, 13:26
(stat.1).... (a^4•b^4•c^4)=(a^2•b^4•c^6) —> (a^4•b^4)/(a^2•b^4)=c^6/c^4 —> a^2•b^0=c^2 —> c^2=a^2 Haha forgot the absolute value though credit to Skyline393 who reminded me so c=a —> c=/+a c=+/4 But why you guys doing some complicated calc. with the statement (1) though I am an advocate of not dividing by an unknown value. Lolx
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Re: If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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30 Apr 2019, 20:30
m1033512 wrote: a = 4 is given , so c can not be 4 , it will take only +4 .
hope this helps
Posted from my mobile device Hi a^2 = c^2 is given and a=4 16= c^2 c can be 4 or 4 to have square 16.
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Re: If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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05 Aug 2019, 07:37
Ans. is E after solving the equation in A, we get c^2=16 => c=4 or4




Re: If a = 4, what is the value of c? (1) (abc)^4 = (ab^2c^3)^2 (2) b = 5
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05 Aug 2019, 07:37






