B = 1.2+2.3+3.4+4.5+...+99.100

3B = 1.2.3 +2.3.3+ 3.4.3+...+99.100.3 
3B = 1.2.3 +2.3(4-1)+ 3.4(5-2)+...+99.100(101-98) 
3B = 1.2.3 +2.3.4-1.2.3+ 3.4.5-2.3.4+...+99.100.101-98.99.100 
3B = 99.100.101

3B = 999900 
B = 999900 : 3

B = 333300

A= 1-2+3-4+4-5+...+99-100

A = (1-2) + (3-4) + (4-5) + ... + (99-100)

A = (-1) + (-1) + (-1) + ...+ (-1)

A = (-1).50

A = 1

a = 0 

b  0 

nhớ ****

Part 1 : Complete each sentence. Use only ONE word. There is one example

Example : I usually get up ...at... 5.30.

1. The weather is nice yesterday.

2. Minh likes watching TV.

3. It's very kind of you to help me.

4. We can see a lot of trees and flowers in the park.

5.             Nam : What do you do, Mai?

                Mai   : I'm a student

Part 2 : Circle A, B, or C to complete the sentence

1.    Tom  : Why don't we go to the zoo this Sunday morning?

        Mary : ....................................................................................

                            A. You are well

                            B. Because I don't like animals

                            C. That's a good idea

2.     Minh : You look tired. What's wrong with you, Ba?

         Ba    :.........................................................................

                             A. I had a headache

                             B. I got some books

                             C. I took a day - off

3.      Is her face round ............................. oval?

                   A. and                            B. or                                 C. but

4.       How ....................... is it from here to your school?

                   A. often                           B. much                           C. far

5.       What ............................ your little sister .......................... in the evening?

                   A. does / do                    B. do / do                        C. do / does