R and K together can build a wall in 20 days, K and M can build the same wall in 30 days and M and R can build the same wall in 24 days. In how many days can all three of them complete the same wall while working together ?

Let R, K, M be the fraction of work each person completes in one day. We have: R+K = 1/20, K+M = 1/30, M+R = 1/24. Adding all three: 2(R+K+M) = 1/20 + 1/30 + 1/24 = 6/120 + 4/120 + 5/120 = 15/120 = 1/8. Therefore, R+K+M = 1/16, meaning all three together complete 1/16 of the wall per day, so the work is finished in 16 days.