Explanation: In P, the primes that occurs are 2, 3, 5, 7.
In Q, there is no 2
So, the HCF of P Q , has powers of only 3, 5 and 7.
In P, 3 comes from 6, 12, 18. So, 3^{4} is the greatest power of 3 in prime factorisation of P . While in Q, 3 comes from 3, 9, 15.
So, 3^{4} is also in prime factorisation of Q.
Similarly 5^{2} is the greatest power of 5 for both P and Q and 7^{1} is the greatest power of 7 for both P and Q.
Hence, HCF of P and Q is (3^{3})(5^{2})(7).