Bunuel
The least common multiple of positive integers p and q is 630. if the greatest common factor of P and Q is 18, what is P - Q?
(1) P is a multiple of 35
(2) The GCD of Q and 35 is 1
\(630 = 3 * 3*2*5*7\)
Possible values of P and Q keeping in mind that HCF cannot be anything other than \(3 * 3 *2\)
Case 1:
P \(= 3 * 3*2*5*7\)
Q \(= 3 * 3*2\)
Case 2:P \(= 3 * 3*2\)
Q \(= 3 * 3*2*5*7\)
Case 3:P \(= 3 * 3*2*5\)
Q \(= 3 * 3*2*7\)
All of the above values of P and Q are the
ONLY cases that will give a LCM of \(630\) and HCF of \(18\), we just need to find the correct values of P and Q to arrive at P-Q.
(1) P is a multiple of \(35\) : This is only possible with case \(1\) hence we know P \(= 3 * 3*2*5*7\) and Q \(= 3 * 3*2\)
We can find P-Q.
SUFF.(2) The GCD of Q and \(35\) is \(1\) :
This tells us that \(7\) and \(5\) are
NOT part of Q hence \(7 \)and \(5\) must be part of P.
Hence P \(= 3 * 3*2*5*7\) and Q\(= 3 * 3*2\)
We can find P-Q.
SUFF.Ans D
Hope it's clear.