You are right, a and b need not be different prime numbers but rather two different integers greater than 1.
Here's a nice rule to keep in mind.: If a and b are two positive integers that have a common factor of c, the remainder when a is divided by b must be a multiple of c.
For example, when a multiple of 18 is divided by 30, the remainder must be a multiple of 6 (i.e. 0,6,12,18 or 24) , since GCF(18,30) = 6.
Similarly, when a multiple of 155 is divided by 210, the remainder must be a multiple of 5 (i.e. 0 , 5 , 10 ,..., 205) since GCF (155,210) = 5.
Question: If x is a positive multiple of 38, and r is the remainder when x is divided by 54, how many possible values of r are greater than 46?
Kevin Armstrong
GMAT Instructor
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Madrid