If 10^a * 3^b * 5^C =450^n, what is the value of c?
(1) a is 1.
(2) b is 2.
Source: Veritas
How come the OA is E???
Thanks
confused about this problem..Power problem
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- GMATGuruNY
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Statements combined:Mo2men wrote:If 10^a * 3^b * 5^C =450^n, what is the value of c?
(1) a is 1.
(2) b is 2.
Case 1: n=0, with the result that (10^a)(3^b)(5^c) = 1
Substituting a=1 and b=2 into (10^a)(3^b)(5^c) = 1, we get:
(10¹)(3²)(5^c) = 1
5^c = 1/90
c = a very ugly number.
Case 2: n=1, with the result that (10^a)(3^b)(5^c) = 450
Substituting a=1 and b=2 into (10^a)(3^b)(5^c) = 450, we get:
(10¹)(3²)(5^c) = 450
5^c = 5
c = 1.
Since c can be different values, the two statements combined are INSUFFICIENT.
The correct answer is E.
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- Jay@ManhattanReview
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The trap in this question is your thinking that a, b, c, and n are integers. This is bolstered more by the information given in the statements: a = 1 and b = 2. However, we must not assume that a, b, c, and n all are integers.Mo2men wrote:If 10^a * 3^b * 5^C =450^n, what is the value of c?
(1) a is 1.
(2) b is 2.
Source: Veritas
How come the OA is E???
Thanks
We are given that 10^a * 3^b * 5^C = 450^n;
Doing prime factorization, we get 2^a * 3^b * 5^(a+c) = 2^n * 3^(2n) * 5^(2n)
The second trap is the value of n would only be determined by a, b, and/or c, i.e. n itself cannot have any value.
Let us discuss each statement one by one.
S1: a = 1
By 2^1 * 3^b * 5^(1+c) = 2^n * 3^(2n) * 5^(2n)
We see that the exponent (a=1) of 2 on the LHS should be equal to the exponent (n) of 2 on the RHS, thus n = 1, and 1 + c = 2n = 2*1 = 2 => c = 1. However, we cannot conclude that the unique value of c =1.
What is n = 0?
In that case, 2^1 * 3^b * 5^(1+c) = 1. The value of c would is indeterminable. Insufficient.
S2: We need not discuss S2. Its fate is the same as that of S1.
S1 and S2: We already have c = 1 from S1.
Let us find out its value if n = 0.
If a = 1 and b = 2, 2^1 * 3^2 * 5^(1+c) = 1
=> 2*9*5*5^c = 1
=> 90 * 5^c = 1 => 5^c = 1/90
=> c < 1; there is no need to calculate the value of c, we need to be assured that its other than 1.
=> c = 1 or c < 1. Insufficient.
Answer: E
Hope this helps!
-Jay
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- crackverbal
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Hi Mo2men,
Here it is easy to jump into conclusion saying both statements together sufficient.
But that's the trick is, here they have not talked about whether a , b and c are integers.
So obviously each statements alone are not sufficient.
Considering together,
Just ask yourself there are 4 unknowns and you know the value of 2 unknowns from the statements.
But still nothing about c and n.
So just be careful, since no condition whether they are integers are not,
we can have n = 1, c = 1
or we can have n = 0, where we have a different c value.
So the answer is E.
Remember if nothing mentioned about the values, then the values could be any real number.
Hope this clear.
Here it is easy to jump into conclusion saying both statements together sufficient.
But that's the trick is, here they have not talked about whether a , b and c are integers.
So obviously each statements alone are not sufficient.
Considering together,
Just ask yourself there are 4 unknowns and you know the value of 2 unknowns from the statements.
But still nothing about c and n.
So just be careful, since no condition whether they are integers are not,
we can have n = 1, c = 1
or we can have n = 0, where we have a different c value.
So the answer is E.
Remember if nothing mentioned about the values, then the values could be any real number.
Hope this clear.
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- crackverbal
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Hi Mo2men,
Here it is easy to jump into conclusion saying both statements together sufficient.
But that's the trick is, here they have not talked about whether a , b and c are integers.
So obviously each statements alone are not sufficient.
Considering together,
Just ask yourself there are 4 unknowns and you know the value of 2 unknowns from the statements.
But still nothing about c and n.
So just be careful, since no condition whether they are integers are not,
we can have n = 1, c = 1
or we can have n = 0, where we have a different c value.
So the answer is E.
Remember if nothing mentioned about the values, then the values could be any real number.
Hope this clear.
Here it is easy to jump into conclusion saying both statements together sufficient.
But that's the trick is, here they have not talked about whether a , b and c are integers.
So obviously each statements alone are not sufficient.
Considering together,
Just ask yourself there are 4 unknowns and you know the value of 2 unknowns from the statements.
But still nothing about c and n.
So just be careful, since no condition whether they are integers are not,
we can have n = 1, c = 1
or we can have n = 0, where we have a different c value.
So the answer is E.
Remember if nothing mentioned about the values, then the values could be any real number.
Hope this clear.
Join Free 4 part MBA Through GMAT Video Training Series here -
https://gmat.crackverbal.com/mba-throug ... video-2018
Enroll for our GMAT Trial Course here -
https://gmatonline.crackverbal.com/
For more info on GMAT and MBA, follow us on @AskCrackVerbal
https://gmat.crackverbal.com/mba-throug ... video-2018
Enroll for our GMAT Trial Course here -
https://gmatonline.crackverbal.com/
For more info on GMAT and MBA, follow us on @AskCrackVerbal