Quiz: Time & Work

A does work in 10 days, B in 15. Together:

A=12d, B=18d; A worked 4d then left. B finishes in:

6 men build wall in 20d; how many for 15d?

A=20d, B=25d, C=30d together:

Pipes A=6h fill; B=8h empty. Both open, tank fills in:

A twice as good as B; together 12d. B alone:

16 men or 20 women. Together 8 men+10 women take:

A can finish in 15 days. He works 5, then B joins & they finish in 4 more. B alone:

Tap A fills in 4h, B in 6h. Both for 2h then A closed. B finishes in:

A+B=8d; A alone=12d. B alone: