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M20-10

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M20-10 [#permalink]

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If \(N\) is a two-digit positive integer, what is the value of its tens digit?


(1) \(2N\) is a two-digit integer whose tens digit is 7

(2) The tens digit of \((N - 9)\) is 2
[Reveal] Spoiler: OA

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Statement (1) by itself is sufficient. \(2N\) can be any of the five numbers: 70, 72, 74, 76, 78. In any of these cases the tens digit of \(N\) is 3.

Statement (2) by itself is insufficient. Consider \(N = 30\) (the answer is 3) and \(N = 29\) (the answer is 2).


Answer: A
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New post 14 Jun 2016, 09:12
I don't agree with the explanation. If the Number is 30 and you substract it by 9 you get 21 and hence the tens digit is 2; Similarly the number 29 - 9 =20 and the tens digit is 2 again

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M20-10 [#permalink]

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New post 14 Jun 2016, 09:16
parmarankita26 wrote:
I don't agree with the explanation. If the Number is 30 and you substract it by 9 you get 21 and hence the tens digit is 2; Similarly the number 29 - 9 =20 and the tens digit is 2 again


Hi,

this is exactly the reason why statement II is not sufficient alone - you should take N as initial value 30 and 29 and not the answer N-9..

The explanation also is the same so why you don't agree to it?
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New post 14 Jun 2016, 09:17
parmarankita26 wrote:
I don't agree with the explanation. If the Number is 30 and you substract it by 9 you get 21 and hence the tens digit is 2; Similarly the number 29 - 9 =20 and the tens digit is 2 again


We need to find tens digit of N. In one case its 3 (N=30) and in another its 2 (29).
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Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

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Re: M20-10 [#permalink]

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New post 26 Sep 2017, 05:56
Bunuel could you solve this question mathematically

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Re: M20-10 [#permalink]

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New post 26 Sep 2017, 11:29
If NN is a two-digit positive integer, what is the value of its tens digit?


(1) 2N is a two-digit integer whose tens digit is 7

(2) The tens digit of (N−9)(N−9) is 2

Sol-
A- As given in option A ten digit is 7,this is only possible when we have 3 as Unit digit if it is able to create one carry to ten digit(30*2=60 -34*2=6_ but from 35*2 to 39*2= 7_
With this logic ,we are left with options- 35,36,37,38,39 only. Hence,for all options,Ten digit is-3-Sufficient
B- Subtract all above choices with 9 and you will get two options as: 2_ or 30 . Insufficient
Hence, Option A

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Re: M20-10 [#permalink]

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New post 26 Sep 2017, 19:03
2N can be any of the five numbers: 70, 72, 74, 76, 78, since the tens digit is 7 and the number is an even number (multiplied by 2). In any of these cases the tens digit of N is 3. Hence, Statement (1) by itself is sufficient.

Now from statement 2:

Consider N=30, the tens digit is 3 and for N=29 the tens digit is is 2. Hence, Insufficient

Answer: A

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Re: M20-10   [#permalink] 26 Sep 2017, 19:03
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