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by joyseychow » Thu Aug 13, 2009 8:06 pm
If n is a multiple of 5, n=p^2q, where p and q are prime numbers. Which of the following must be a multiple of 25?

A. p^2
B. q^2
C. pq
D. p^2q^2
E. p^3q


Easy one, but I didn't get right. Why B cannot be the answer?
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by tohellandback » Thu Aug 13, 2009 8:45 pm
answer is D
n=p^2q
either p or q can be 5
clearly P^2*q^2 must be divisible by 25.

B cannot be the answer because
if p is 5 then q can be any prime number. 3,7, etc.
in that case p^2 will not be divisible by 25
The powers of two are bloody impolite!!
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by ankitns » Fri Aug 14, 2009 5:33 am
tohellandback wrote:answer is D
n=p^2q
either p or q can be 5
clearly P^2*q^2 must be divisible by 25.

B cannot be the answer because
if p is 5 then q can be any prime number. 3,7, etc.
in that case p^2 will not be divisible by 25

q cannot be 5...plug in the numbers...if p = 2 and q = 5...we get
n = 2^10 = 1024..not a multiple of 5....

n can only be a multiple of 5 only if p is 5...and if p is a multiple of 5 then p^2 must be a multiple of 25...

Hence the answer is A[spoiler][/spoiler]
Attempt 1: 710, 92% (Q 42, 63%; V 44, 97%)
Attempt 2: Coming soon!
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by tohellandback » Fri Aug 14, 2009 5:40 am
ankitns wrote:
tohellandback wrote:answer is D
n=p^2q
either p or q can be 5
clearly P^2*q^2 must be divisible by 25.

B cannot be the answer because
if p is 5 then q can be any prime number. 3,7, etc.
in that case p^2 will not be divisible by 25

q cannot be 5...plug in the numbers...if p = 2 and q = 5...we get
n = 2^10 = 1024..not a multiple of 5....

n can only be a multiple of 5 only if p is 5...and if p is a multiple of 5 then p^2 must be a multiple of 25...

Hence the answer is A[spoiler][/spoiler]
with p=2, how r u getting n=2^10
it will be n=2^2*5
..or hey may be you think its n=P^(2q)
The powers of two are bloody impolite!!
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by ankitns » Fri Aug 14, 2009 7:22 am
yes..I was thinking n=p^(2q)...

joyseychow: Could you please clarify whether the question states

n=p^(2q)

or

n=(p^2) * q


Thanks.

tohellandback wrote:
ankitns wrote:
tohellandback wrote:answer is D
n=p^2q
either p or q can be 5
clearly P^2*q^2 must be divisible by 25.

B cannot be the answer because
if p is 5 then q can be any prime number. 3,7, etc.
in that case p^2 will not be divisible by 25

q cannot be 5...plug in the numbers...if p = 2 and q = 5...we get
n = 2^10 = 1024..not a multiple of 5....

n can only be a multiple of 5 only if p is 5...and if p is a multiple of 5 then p^2 must be a multiple of 25...

Hence the answer is A[spoiler][/spoiler]
with p=2, how r u getting n=2^10
it will be n=2^2*5
..or hey may be you think its n=P^(2q)
Attempt 1: 710, 92% (Q 42, 63%; V 44, 97%)
Attempt 2: Coming soon!
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by joyseychow » Sun Aug 23, 2009 2:00 am
ankitns wrote:yes..I was thinking n=p^(2q)...

joyseychow: Could you please clarify whether the question states

n=p^(2q)

or

n=(p^2) * q


Thanks.

tohellandback wrote:
ankitns wrote:
tohellandback wrote:answer is D
n=p^2q
either p or q can be 5
clearly P^2*q^2 must be divisible by 25.

B cannot be the answer because
if p is 5 then q can be any prime number. 3,7, etc.
in that case p^2 will not be divisible by 25

q cannot be 5...plug in the numbers...if p = 2 and q = 5...we get
n = 2^10 = 1024..not a multiple of 5....

n can only be a multiple of 5 only if p is 5...and if p is a multiple of 5 then p^2 must be a multiple of 25...

Hence the answer is A[spoiler][/spoiler]
with p=2, how r u getting n=2^10
it will be n=2^2*5
..or hey may be you think its n=P^(2q)
Sorry. It's n=(p^2) * q.
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by real2008 » Mon Aug 24, 2009 11:05 am
joyseychow wrote:
ankitns wrote:yes..I was thinking n=p^(2q)...

joyseychow: Could you please clarify whether the question states

n=p^(2q)

or

n=(p^2) * q


Thanks.

tohellandback wrote:
ankitns wrote:
tohellandback wrote:answer is D
n=p^2q
either p or q can be 5
clearly P^2*q^2 must be divisible by 25.

B cannot be the answer because
if p is 5 then q can be any prime number. 3,7, etc.
in that case p^2 will not be divisible by 25

q cannot be 5...plug in the numbers...if p = 2 and q = 5...we get
n = 2^10 = 1024..not a multiple of 5....

n can only be a multiple of 5 only if p is 5...and if p is a multiple of 5 then p^2 must be a multiple of 25...

Hence the answer is A[spoiler][/spoiler]
with p=2, how r u getting n=2^10
it will be n=2^2*5
..or hey may be you think its n=P^(2q)
Sorry. It's n=(p^2) * q.
then answer is D
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