Time and Work on Arithmetic Aptitude related Questions and Answers

Question :   A, B and C can do a piece of work in 15 days, 10 days and 6 days respectively. How long will they take to do it, if all the three work together? 1. 7 days 2. 5 days 3. 3 days 4. 2.5 days Answer :   3 - 3 days