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@devashish2407Asked: If x ≠ 1 and x is a common factor of integer y and odd integer z, is x a prime number?

Let y = xk; z = xm

(1) –85 < 10 – y < –80
-95 < -y < - 90
90 < y < 95
y = {91,92,93,94}
91 = 7*13
92 = 2*2*23
93 = 3*31
94 = 2*47
Since z is unknown
NOT SUFFICIENT

(2) 140 < z < 145
z = {141,143}
141 = 3*47
143 = 11*13
Since y is unknown
SUFFICIENT

(1) + (2) 
(1) –85 < 10 – y < –80
-95 < -y < - 90
90 < y < 95
y = {91,92,93,94}
(2) 140 < z < 145
z = {141,143}
x = {3,11,13,47} : All are prime numbers 
SUFFICIENT

IMO C
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If in statement two, all the factors of 141, and 143 are prime (which they are), and we know that one of them is x, the common factor, then why would the official answer not be B. The set of factors outlined in 2 is the same as in your conclusion that it is C (3,11,13, 47). Can anyone elaborate?
Kinshook
@devashish2407Asked: If x ≠ 1 and x is a common factor of integer y and odd integer z, is x a prime number?

Let y = xk; z = xm

(1) –85 < 10 – y < –80
-95 < -y < - 90
90 < y < 95
y = {91,92,93,94}
91 = 7*13
92 = 2*2*23
93 = 3*31
94 = 2*47
Since z is unknown
NOT SUFFICIENT

(2) 140 < z < 145
z = {141,143}
141 = 3*47
143 = 11*13
Since y is unknown
SUFFICIENT

(1) + (2)
(1) –85 < 10 – y < –80
-95 < -y < - 90
90 < y < 95
y = {91,92,93,94}
(2) 140 < z < 145
z = {141,143}
x = {3,11,13,47} : All are prime numbers
SUFFICIENT

IMO C
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mattisweb
If in statement two, all the factors of 141, and 143 are prime (which they are), and we know that one of them is x, the common factor, then why would the official answer not be B. The set of factors outlined in 2 is the same as in your conclusion that it is C (3,11,13, 47). Can anyone elaborate?


Statement (2) only fixes z (141 or 143) but gives no restriction on y. Since x must be a common factor of both y and z, we cannot guarantee from (2) alone that x will always be prime.

For example, if z = 143 and y = 143, then the common factors are {1, 11, 13, 143}. Here x could be 143, which is not prime. However if x is 11, then it is a prime.

Because both scenarios are possible, Statement (2) alone is not sufficient.
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Bunuel

In that case we have two common factors (X), that is 3,13 or 47.

So as we dont have a unique common factor isnt the statemnt insufficinet despite them being all prime?

y = {91,92,93,94}
91 = 7*13
92 = 2*2*23
93 = 3*31
94 = 2*47

z = {141,143}
141 = 3*47
143 = 11*13

Bunuel


Statement (2) only fixes z (141 or 143) but gives no restriction on y. Since x must be a common factor of both y and z, we cannot guarantee from (2) alone that x will always be prime.

For example, if z = 143 and y = 143, then the common factors are {1, 11, 13, 143}. Here x could be 143, which is not prime. However if x is 11, then it is a prime.

Because both scenarios are possible, Statement (2) alone is not sufficient.
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quiaitaque
Bunuel

In that case we have two common factors (X), that is 3,13 or 47.

So as we dont have a unique common factor isnt the statemnt insufficinet despite them being all prime?

y = {91,92,93,94}
91 = 7*13
92 = 2*2*23
93 = 3*31
94 = 2*47

z = {141,143}
141 = 3*47
143 = 11*13



We are asked to find whether x is prime, not the exact value of x.
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