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Im not sure that Statement 1 is sufficient on it's own. All we know from st1 is that N has prime factors of 2,5,7, and possibly others. From this, N could be 14, or 70 ...

But statement 2 is good because it tells you exactly the value of N. Keep in mind you dont have to figure it out, but you just have to know that if you had time, you could get a value for N and see what its units digit is.

St. 1 : 14 = 2 * 7, 35 = 5 * 7, hence, 2,5,7 are factors of N. If N=70, 35 * 2 or 14 * 5 If N=105, 35*3, 14 isn't a factor of 105. If N = 140, 35 * 4, 14 * 10

Thus, when 14 and 35 are factors of N, the unit's digit is always 0 ! Hence, Sufficient.

St.2 : N=(2^5)(3^2)(5^7)(7^6)

As you have 2*5 here, the unit's digit will always be 0. Hence, Sufficient.

Re: If N is a positive Integer, is the units digit of N equal to [#permalink]

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10 May 2014, 08:51

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Re: If N is a positive Integer, is the units digit of N equal to [#permalink]

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29 Sep 2015, 22:13

Bunuel wrote:

patternpandora wrote:

meaglesp345 wrote:

If N is a positive Integer, is the units digit of N equal to zero?

(1) 14 and 35 are factors of N (2) N = (2^5)(3^2)(5^7)(7^6)

Bunnel: If you could throw some light particularly on statement (1), it would be great.

I am still not clear how even statement (2) ensures that unit digit will be zero.

If N is a positive Integer, is the units digit of N equal to zero?

(1) 14 and 35 are factors of N --> N is divisible by 2 and 5, hence it's divisible by 10 --> the units digit must be 0. Sufficient.

(2) N = (2^5)(3^2)(5^7)(7^6). The same here 2 and 5 ensure that N is divisible by 10. Sufficient.

Answer: D.

Hope it's clear.

I opted B.

Bunnel..I am having doubts with statement 1. It just says 14 & 35 are factors of N, but it doesn't specify whether they are the only factors. If they aren't, then 1 isn't sufficient on its own. How can we infer that they are the only factors, when it's not clearly specified.
_________________

Bunnel: If you could throw some light particularly on statement (1), it would be great.

I am still not clear how even statement (2) ensures that unit digit will be zero.

If N is a positive Integer, is the units digit of N equal to zero?

(1) 14 and 35 are factors of N --> N is divisible by 2 and 5, hence it's divisible by 10 --> the units digit must be 0. Sufficient.

(2) N = (2^5)(3^2)(5^7)(7^6). The same here 2 and 5 ensure that N is divisible by 10. Sufficient.

Answer: D.

Hope it's clear.

I opted B.

Bunnel..I am having doubts with statement 1. It just says 14 & 35 are factors of N, but it doesn't specify whether they are the only factors. If they aren't, then 1 isn't sufficient on its own. How can we infer that they are the only factors, when it's not clearly specified.

The question asks whether the units digit of N equals to zero. From (1) N is divisible by 2 and 5, hence it's divisible by 10, which means that the units digit of N is 0. We don't care about other factors of N at all.
_________________

Re: If N is a positive Integer, is the units digit of N equal to [#permalink]

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31 Jan 2017, 23:06

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If you take apart 14 and 35 say- 2 x 7 x 5 x 5 - is this correct method for making that conclusion?

N is divisible by 14, so it's divisible by 2. N is divisible by 35, so it's divisible by 5.

Thus, it's divisible by 10.

Generally if a positive integer is divisible by positive integers x and y, then it must be divisible by the least common multiple of x and y. So, N above must be divisible by the LCM(14, 35), so by 70.
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If N is a positive Integer, is the units digit of N equal to zero?

(1) 14 and 35 are factors of N (2) N = (2^5)(3^2)(5^7)(7^6)

We need to determine whether the units digit of a positive integer N is zero. If N has a units digit of zero, then N must be divisible by 10. In other words, N must be divisible by both 2 and 5.

Statement One Alone:

14 and 35 are factors of N.

Since 14 is divisible by 2 and 35 is divisible by 5, N is divisible by both 2 and 5, and thus it has a units digit of zero. Statement one alone is sufficient. We can eliminate answer choices B, C, and E.

Statement Two Alone:

N = (2^5)(3^2)(5^7)(7^6)

We see that N is divisible by both 2 and 5 and thus has a units digit of zero. Statement two alone is also sufficient.

Answer: D
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