mba878 wrote:
PrepTap wrote:
What is the GCD of a and b?
1. The only common prime factor of a and b is even.
2. b/p (where p is a prime number) and a don’t have a common prime factor.
This question is a part of the series of original questions posted every weekday by PrepTap. Follow us to receive more questions like this.The answer to the above question should be E And not C.
From statement 1 one can infer that 2 is a common factor to both a & b but what power o 2 goes into both a & b cannot be
determined from the given inormation.
From Statement 2 again one doesnt have enough information to evaluate the the GCD.
same follows when we combine A & B, hence E must be the answer.
Hi mba878
From the first statement, we learn that the common prime factor is 2. But we don't know whether 2 or 2^2 or 2^3.... is common between a and b.
The second statement says b/p and a don't have a common prime factor, so p (=2^1) must've been the common factor of a and b.
Essentially when we combine the two statements, we learn that 2 is the only common prime factor and only the first power of 2 is a factor of b.
If that weren't the case, b/2 would still contain at least one power of 2 and there would be a common factor between b/2 and a, which goes against statement 2.
As an example, take a = 6 and b = 10.
Their only common prime factor is 2, which is even.
And 6 and 10/2 (=5) don't have a common prime factor.
So we can easily say that 2 is the GCD here.