1/18 + 1/30 = 8/90 = 4/45
45/4 = 11 ¼ *2 = 22 1/2 days
A can do a job in 18 days and B can do it in 30 days. A and B working together will finish twice the amount of work in ------- days?
1: 22 1/8
2: 22 1/2
3: 22 1/1
4: 22 1/5
5: 22 1/9