Ans. of 14 is 6. not 1.
Joint Rate of John and Jane= 1/20+1/12 = 2/15
John does in 4 days = 1/20*4= 1/5
left 4/5 part is done by both them.
So together they work = 4/5*15/2 = 6 Ans.
I am student of everyone-baten
PSof OG solved by GC members: http://gmatclub.com/forum/collection-ps-with-solution-from-gmatclub-110005.html
DS of OG solved by GC members: http://gmatclub.com/forum/collection-ds-with-solution-from-gmatclub-110004.html
100 GMAT PREP Quantitative collection http://gmatclub.com/forum/gmat-prep-problem-collections-114358.html
Collections of work/rate problems with solutions http://gmatclub.com/forum/collections-of-work-rate-problem-with-solutions-118919.html
Mixture problems in a file with best solutions: http://gmatclub.com/forum/mixture-problems-with-best-and-easy-solutions-all-together-124644.html