The McGraw-Hill Workbook by Mark Connelly    
Chapter 20: Avoiding Confusing Shifts Ex.20-1 pp. 323-324

Rewrite each sentence to eliminate needless shifts. Be advised that these sentences may be corrected in different ways.

1. Naturally anyone hearing this question would not know how he or she could begin to answer.

2. If there were a simple solution, students would not find it.

3. Shaking their heads, the students had no idea how to begin to answer.

4. If Fermi were making a joke, few people would remember it.

5. Fermi wanted his students to realize that anyone could arrive at a reasonable answer if they would make a series of assumptions.

6. If one knew that there were three million people in Chicago, one could assume that the average household had four members.

7. If you were to assume that there was one piano for every three households, you could assume there were 
    250,000 pianos in Chicago.

8. If you assume that each piano is tuned once a decade, then there would be 25,000 tunings a year.

9. If you assumed the average piano tuner serviced four pianos a day, you would guess that twenty tunings were performed each week.

10. Since most people take a two-week vacation, the average piano tuner works fifty weeks and services one- thousand pianos a year.

11. From these assumptions students would make their estimates that there are twenty-five piano tuners in Chicago.

12. Naturally, students realize that they have rough estimates with which to work.

13. Students understand that there assumptions could be wrong; there could be only ten or more than fifty piano tuners.

14. But as Fermi demonstrated with the Yellow Pages, twenty-five was a good estimate.

15. Fermi wanted to show that one could probe the unknown and could achieve a ballpark figure through making a chain of assumptions.

16. Any of the assumptions students made could be wrong; students might estimate that one in three homes had a piano when the real figure was one in ten.

17. But since it was unlikely that one would consistently overestimate or underestimate, one miscalculation was cancelled out by another.

18. Thus, even if one made a wild guess, one might have ultimately arrived at a reasonable answer.

19. Someone trying to fathom a vast unknown subject may find that he or she could make use of this system of educated calculations.

20. Fermi, who unlocked the secret of the atom, was able to demonstrate to us complete thinking processes in terms we could understand.

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