11. Every one of the cakes is/are gone.
12. Fifty percent of the pie have/has disappeared.
13. Fifty percent of the pies have/has disappeared.
14. One-third of the city is/are unemployed.
15. One-third of the people is/are unemployed.
16. All of the pie is/are gone.
17. All of the pies is/are gone.
18. Some of the pie is/are missing.
19. Some of the pies is/are missing.
20. None of the garbage was/were picked up.