The user-friendly version of this content is available here.
The following content is copyright (c) 2009-2013 by Goods of the Mind, LLC.
This problem trains for: SAT-I, AMC-8, GMAT.
Which one of the pairs of numbers listed is not a pair of numbers that add up to 20 and have a greatest common divisor (factor) of 1 (in other words, they are coprime)?
this is the defective pair.