If R is the remainder when positive integer is divided by 7, what is the value of r?
1) When n is divided by 21, the reaminder is an odd number.
2) When n is divided by 28, the remainder is 3.
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If R is the reaminder when positive integer is divided by 7.
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n mod 7 = ?
1. n mod 21 = odd number
Since we cannot be sure what this odd number is, the corresponding value of r is also not identifiable.
Think of different values of N, such as 22 and 40 that would yield different odd remainders and correspondingly different values of r.
INSUFFICIENT
2. n mod 28 = 3
Since 28 is a multiple of 7, you can be sure that a (multiple of 28) + 3, will produce a number that also has a remainder of 3 when divided by 7.
Thus r = 3
SUFFICIENT
Pick B
1. n mod 21 = odd number
Since we cannot be sure what this odd number is, the corresponding value of r is also not identifiable.
Think of different values of N, such as 22 and 40 that would yield different odd remainders and correspondingly different values of r.
INSUFFICIENT
2. n mod 28 = 3
Since 28 is a multiple of 7, you can be sure that a (multiple of 28) + 3, will produce a number that also has a remainder of 3 when divided by 7.
Thus r = 3
SUFFICIENT
Pick B
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for a question like this one, instead of doing algebra think of it like this:
instead of: R is the remainder when positive integer is divided by 7
think like this: N is 3 more than a multiple of 7
now (1) is clearly insufficient.
n is n+odd multiple of 21. clearly insufficient as it could be anything.
(2)
n = 3 more than a multiple of 28
28 itself is a multiple of 7, so we can simply say n = 3 more than a multiple of 7.
therefore R = 3
hence (B).
instead of: R is the remainder when positive integer is divided by 7
think like this: N is 3 more than a multiple of 7
now (1) is clearly insufficient.
n is n+odd multiple of 21. clearly insufficient as it could be anything.
(2)
n = 3 more than a multiple of 28
28 itself is a multiple of 7, so we can simply say n = 3 more than a multiple of 7.
therefore R = 3
hence (B).
"Do not confuse motion and progress. A rocking horse keeps moving but does not make any progress."
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- Alfred A. Montapert, Philosopher.