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RMD007
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If a and b are non negative integers, what is remainder when 11^a/b Updated on: 21 Jan 2017, 22:06
Originally posted by RMD007 on 21 Jan 2017, 11:03.
Last edited by RMD007 on 21 Jan 2017, 22:06, edited 1 time in total.
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Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

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25% (medium)

Question Stats:

73% (00:48) correct 27% (00:43) wrong based on 169 sessions

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If a and b are non negative integers, what is remainder when \(\frac{(11^a)}{b}\)?

1. a = 2
2. b = 10

Source : Self Made :)
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B
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If a and b are non negative integers, what is remainder when 11^a/b 21 Jan 2017, 19:03
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RMD007
If a and b are non negative integers, what is remainder when \(\frac{(11^a)}{b}\)?

1. a = 2
2. b = 10
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Dear RMD007

I'm happy to respond. :-) This is a great problem!

You may find the discussion in this blog article germane:
GMAT Quant: Difficult Units Digits Questions

You see, any two numbers with units digits both equal to 1 will have a product with a units digit of 1. Thus, for 11, 21, 91, or any other number with a units digit of 1, all the powers of that number will have units digits of 1. We know for a fact that, regardless of the value of a, every possible \(11^a\) will have a units digit of 1.

Statement #1 is obviously insufficient, because we don't know B.

With statement #2, we are dividing some unknown power of 11 by 10. Since every power of 11 has a units digit of 1, the remainder when we divide by 10 has to be 1. With this statement, we get a definitive answer to the prompt question, so the second statement is sufficient.

OA = (B)

Does all this make sense?
Mike :-)
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If a and b are non negative integers, what is remainder when 11^a/b 21 Jan 2017, 20:55
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RMD007
If a and b are non negative integers, what is remainder when \(\frac{(11^a)}{b}\)?

1. a = 2
2. b = 10
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Hi

Two points in such Qs..
Non negative integers would also include 0 and any number to the power of 0 will be 1..
If divisor is 2,5 or 10, it is sufficient to know just the units digit..

So here 11 to the power of anything, 0 and above, will have units digit as 1..
And when we are given denominator as 10, even if it was 2 or 5, remainder will be 1
Suff

B
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If a and b are non negative integers, what is remainder when 11^a/b 22 Jan 2017, 05:21
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If a and b are non negative integers, what is remainder when \(\frac{(11^a)}{b}\)?

1. a = 2

Let b=11 ..........11^2/11.....reminder is 0

Let b= 2............11^2/11.....reminder is 1

Insufficient

2. b = 10

let a= 1...............11/10..........reminder is 1

a=2................121/10........reminder is 1


Any power raised to 11 with make this number greater than 10 or its multiple of 10 by 1. Always reminder is 1

Sufficient

Answer: B
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If a and b are non negative integers, what is remainder when 11^a/b 11 Sep 2025, 05:33
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