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11 Nov 2019, 04:43
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B
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Difficulty:
85%
(hard)
Question Stats:
51% (02:35) correct
49%
(02:14)
wrong
based on 240
sessions
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If P and Q are positive integers and Q = 10 + 4P, find the GCD of P and Q
(1) Q = 10 x, where x is a positive integer
(2) P = 10 y, where y is a positive integer
Are You Up For the Challenge: 700 Level Questions
(1) Q = 10 x, where x is a positive integer
(2) P = 10 y, where y is a positive integer
Are You Up For the Challenge: 700 Level Questions
Pure algebraic questions like this one are no longer part of the GMAT Data Sufficiency syllabus.
For relevant Data Sufficiency questions, please check the Data Sufficiency forum:
Data Sufficiency Forum
Data Sufficiency Forum
11 Nov 2019, 08:15
Kudos
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If P and Q are positive integers and Q = 10 + 4P, find the GCD of P and Q
(1) Q = 10 x, where x is a positive integer
\(10x=10+4p.....4p=10x-10\)
For 10x-10 to be a multiple of 4, x will always be ODD...
so Q=10x=10*3=30....30=10+4p.....4p=20.....p=5.......GCD(30,5)=5
Q=10x=10*5=50....50=10+4p.....4p=40.....p=10.......GCD(50,10)=10
Insuff
(2) P = 10 y, where y is a positive integer
\(P=10+4*10y.....P=10(1+4y)\)
Now, 1+4y is one more than a multiple of y, that is 4y, so 1+4y and y are co-prime, that is they do not have any factors in common..
Thus GCD(10(1+4y),10y) =10
Suff
B
(1) Q = 10 x, where x is a positive integer
\(10x=10+4p.....4p=10x-10\)
For 10x-10 to be a multiple of 4, x will always be ODD...
so Q=10x=10*3=30....30=10+4p.....4p=20.....p=5.......GCD(30,5)=5
Q=10x=10*5=50....50=10+4p.....4p=40.....p=10.......GCD(50,10)=10
Insuff
(2) P = 10 y, where y is a positive integer
\(P=10+4*10y.....P=10(1+4y)\)
Now, 1+4y is one more than a multiple of y, that is 4y, so 1+4y and y are co-prime, that is they do not have any factors in common..
Thus GCD(10(1+4y),10y) =10
Suff
B
12 Nov 2019, 05:11
Kudos
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Bunuel
From 1)
\(10X=10+4P\)
LHS is always be a multiple of 10. For RHS to be a multiple of 10
P= 5n( n is integer) or P=10n(n is integer)
it depends upon P
Not sufficient
From 2)
\(Q=10+40Y\)
Q=50,90,130....always a multiple of 10
P=10Y
GCD=10
SUFFICIENT
B:)
