Sure, let's go through each sentence and identify the errors, then correct them:

1. **Error:** "Geography are fascinating."
**Correction:** "Geography is fascinating."

2. **Error:** "Where is my gloves?"
**Correction:** "Where are my gloves?"

3. **Error:** "Each ticket costed $5."
**Correction:** "Each ticket cost $5."

4. **Error:** "The boy with his dog are here."
**Correction:** "The boy with his dog is here."

5. **Error:** "John or Tom are bringing the car."
**Correction:** "John or Tom is bringing the car."

6. **Error:** "His hair are turning gray."
**Correction:** "His hair is turning gray."

7. **Error:** "Are there anybody at home?"
**Correction:** "Is there anybody at home?"

8. **Error:** "Neither praise nor blame seem to affect him."
**Correction:** "Neither praise nor blame seems to affect him."

9. **Error:** "Three fourths of his fortune were devoted to scientific research."
**Correction:** "Three fourths of his fortune was devoted to scientific research."

10. **Error:** "Two-thirds of these books is novels."
**Correction:** "Two-thirds of these books are novels."

11. **Error:** "There are a car and two vans in front of my house."
**Correction:** "There is a car and two vans in front of my house."

12. **Error:** "Why is the police standing there?"
**Correction:** "Why are the police standing there?"

13. **Error:** "So far everything is all right."
**Correction:** This sentence is actually correct as it is.

14. **Error:** "More men than women is left-handed."
**Correction:** "More men than women are left-handed."

15. **Error:** "Fifty minutes are the maximum length of time allotted for the exam."
**Correction:** "Fifty minutes is the maximum length of time allotted for the exam."

16. **Error:** "None of my classmates speaks Arabic."
**Correction:** This sentence is actually correct as it is.

17. **Error:** "Every student are tested twice a year."
**Correction:** "Every student is tested twice a year."

18. **Error:** "Each of the items in the bill are correct."
**Correction:** "Each of the items in the bill is correct."

19. **Error:** "10 years in prison were too long for him."
**Correction:** "10 years in prison was too long for him."

20. **Error:** "None of the children were awake."
**Correction:** "None of the children was awake."

**Explanation:**

1. "Geography" is a singular noun, so it takes "is."
2. "Gloves" is plural, so it takes "are."
3. "Cost" is the correct past tense form of "cost."
4. The subject "The boy with his dog" is singular, so it takes "is."
5. When subjects are connected by "or," the verb agrees with the nearest subject, which is singular "Tom."
6. "Hair" is considered singular when referring to all the hair on one's head.
7. "Anybody" is singular, so it takes "is."
8. "Neither...nor" constructs take a singular verb.
9. "Three fourths" is considered a singular fraction of "fortune."
10. "Books" is plural, so it takes "are."
11. The subject closest to the verb "There is" is "a car," which is singular.
12. "Police" is a collective noun and takes a plural verb.
13. This sentence is correct as it stands.
14. "Men" and "women" are plural, so the verb should be "are."
15. "Fifty minutes" is considered a singular period of time.
16. This sentence is correct as it stands.
17. "Every student" is singular, so it takes "is."
18. "Each" is singular, so it takes "is."
19. "10 years" is considered a singular period of time.
20. "None" can be singular or plural, but in this context, "was" is more appropriate.