value of k

[kanha81]

If n is a positive integer and k =5.1 x 10^n, what is the value of k ?

(1) 6,000 < k < 500,000

(2) k^2 = 2.601 x 10^9

[Feep]

I arrived at D.

(1) gives the range of k between 6,000 and 500,000. We know that k must equal 5.1, 51, 510, 5100, 51000, 510000, 5100000, etc.; the only number in this set that falls in the given range is 51,000, n is 4. Sufficient.

(2) gives an exact value of k, which therefore gives an exact value of n. Note that the GMAT will not give you a statement which will contradict any information given in the problem description, which means that this will yield an integer value for n. For the curious, it is also n = 4. Sufficient.

D.

[kanha81]

I arrived at D.

(1) gives the range of k between 6,000 and 500,000. We know that k must equal 5.1, 51, 510, 5100, 51000, 510000, 5100000, etc.; the only number in this set that falls in the given range is 51,000, n is 4. Sufficient.

(2) gives an exact value of k, which therefore gives an exact value of n. Note that the GMAT will not give you a statement which will contradict any information given in the problem description, which means that this will yield an integer value for n. For the curious, it is also n = 4. Sufficient.

D.

Thanks Feep! I got stuck in (1).

[tyronetan82]

I don't understand why it is D. Isn't the root of something will result in a positive and a negative value? Such that root 4 is + or - 2..... please enlighten me.