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(1) z is the remainder when positive integer y is divided by positive integer (y - 1) (2) y is not a prime number

Kudos for a correct solution.

statement 1: y is at least one. if y=2 then (y-1) is a factor of y and reminder z is zero. If y=13 then (y-1) is not a factor of y and reminder z is one.

statement 2: clearly not sufficient

1+2) we can eliminate the case in which y=2. z will always be one.

Answer C
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(1) z is the remainder when positive integer y is divided by positive integer (y - 1) (2) y is not a prime number

Kudos for a correct solution.

(1) z is the remainder when positive integer y is divided by positive integer (y - 1) y could be 8. In this case the remainder would be 1 y could also be 2. Here the remainder is 0. Insufficient.

(2) y is not a prime number Nothing is indicated about integer z. Insufficient.

Combined, the remainder will always be 1 as the denominator will always 1 less than the numerator. Sufficient.

(1) z is the remainder when positive integer y is divided by positive integer (y - 1) (2) y is not a prime number

Kudos for a correct solution.

z = ?

(1) z is the remainder when positive integer y is divided by positive integer (y - 1)

Consecutive positive integers y and (y-1) are always co-primes and if y is divided by (y-1) then the remainder will always be 1 y = (y - 1) * 1 + 1

we can try out a few numbers y = 2 , (y-1) = 1, remainder = 1 y = 5 , (y-1) = 4, remainder = 1 y = 10, (y-1) = 9, remainder = 1 y = 2561, (y-1) = 2560, remainder = 1

Hence z = 1 So Stmt (1) is sufficient.

(2) y is not a prime number This gives no information about z Hence Stmt (2) is insufficient

This is an value DS question, where you got an unique value for z. 1). Statement 1 is insufficient. Suppose say y=40 then y-1 is 39. And remainder is 1. If y=16 then y-1 is 15 and again remainder is 1. But if we take y=2 then y-1 is 1. And the remainder is zero because all the numbers are divisible by 1. 2). Statement 2 is insufficient. This doesn’t anything about z. Together sufficient, Statement 2 tells that 2 is not possible. Because its a prime number. So obviously when you divide any number by its predecessor . the quotient is 1 and remainder 1. So z is 1. Together sufficient. So the answer is C.
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This question is a classic “Why Are You Here?” question. Statement 1 may look sufficient if you pick numbers (8 and 7; 15 and 14; 5 and 4 ? the remainder is always 1). But what about 2 and 1? There’s no remainder there, so z would equal 0. Statement 2 tells us that (y - 1) cannot be 1, because y cannot be 2. This takes away that one flaw with statement 1, and means that both statements together are sufficient.
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AT first glance stmt A seems sufficient bUt thats how GMAT tricks us isn't it? if y=2 then y-1=1 and remainder z=0 in this case..but if y= any positive number other than 2 then remainder would be 1.. hence not sufficient. Using statement 2 we have y is not prime so it cant not be equal to 2 definately hence solved. Hence C is the answer. hope the explanation helps.

why can't y be 1, as its not a prime???Thus 1/0---inconclusive. or 9/8,10/9--remainder 1..Thus E @Bunuel@VeritasPrepKarishma Please clarify

y cannot be 1 because in this case y-1=0 and division be 0 is not allowed.

Despite that , Isn't there possibility of distinct answer, leading us to E

No.

(1) says that z is the remainder when positive integer y is divided by positive integer (y - 1). If y=1, no integer can be the remainder when y=1 is divided by y-1=0 because division by 0 is NOT allowed.
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