大概 (dàgài) and 左右 (zuǒyòu)

大概 is generally used to mean "approximately", "more or less", or "something like that". Here's an example:

• 我大概明白你的意思。(I don't understand what you're saying completely but I get the gist.)
• Dialogue:
• A：你打了多少个电话？ (How many phone calls did you make?)
• B1：大概50个。(Approximately 50. The structure is 大概+number+measure word.)
• B2：50个左右。(50 or thereabouts.The structure is number+measure word+左右.) 

Here's another example of how using 大概 and 左右 are approximately the same but have a different connotation:

• A：你的车买了多少钱？
• B1: 大概三十万人民币。(Around 300,000RMB.)
• B2: 三十万人民币左右。(300,000RMB more or less.)

In this example, 大概 implies the speaker is unclear or uncertain about the amount, or perhaps they don't remember. The use of 左右 implies a greater level of accuracy or certainty on the part of the speaker but they don't care to go into greater detail. The listener could press the speaker for more detail, in which case they would follow up with a more exact number if they were able.

Please choose 大概 or 左右 to make each sentence meaningful.

1. 他_________是个中国人。
2. 他走路摇摇晃晃的，_________是醉了。
3. 他_________知道要说些什么。
4. 今天中午有20摄氏度_________。
5. 他30岁_________。
6. UB _________有3000多国际学生。
7. 这辆车很省油，加一次油_________可以用两周。
8. 我今天两点_________到学校。
9. 都两点一刻了，他还没有到，_________是路上堵车。
10. 意大利面，一般要煮9分钟_________。

Please talk about when you usually do the following daily activities.说一说你每天大概什么时候做下面的活动：

1. 起床
2. 洗澡
3. 吃早饭
4. 上班
5. 吃午饭
6. 下班
7. 吃完饭
8. 睡觉

http://chinesepod.com/lessons/being-vague-%E5%A4%A7%E6%A6%82-dagai-%E5%B7%A6%E5%8F%B3-zu%C7%92you-%E4%B8%8A%E4%B8%8B-shangxia
http://www.italki.com/question/39651