Tính hợp lí 1/ (– 37) + 14 + 26 + 37

Tính hợp lí 1/ (– 37) + 14 + 26 + 37

Đề bài: Tính hợp lí

1/ (– 37) + 14 + 26 + 37;

2/ (– 24) + 6 + 10 + 24;

3/ 15 + 23 + (– 25) + ( – 23);

4/ 60 + 33 + (– 50) + (– 33);

5/ (– 16) + ( – 209) + ( – 14) + 209;

6/ (– 12) + ( – 13) + 36 + (– 11);

7/ 300 – (– 200) – (– 120) + 18;

8/ – (– 299) + (– 219) – 401 + 12;

9/ 555 – (– 333) – 100 – 80;

10/ 34 + 35 + 36 + 37 – 14 – 15 – 16 – 17;

11/ 1+ (– 2) + 3 + (– 4) + ..... + 19 + (– 20);

12/ 1 – 2 + 3 – 4 + ... + 99 – 100.

Lời giải:

1/ (– 37) + 14 + 26 + 37

= [(– 37) + 37] + (14 + 26)

= 0 + 40 = 40

2/ (– 24) + 6 + 10 + 24

= (– 24 + 24) + (6 + 10)

= 0 + 16 = 16

3/ 15 + 23 + (– 25) + ( – 23)

= [15 + (– 25) + [23 + (– 23)]

= – 10 + 0 = – 10

4/ 60 + 33 + (– 50) + (– 33)

= [60 + (– 50)] + [33 + (– 33)]

= 10 + 0 = 10

5/ (– 16) + ( – 209) + ( – 14) + 209

= [(– 16) + (– 14)] + [(– 209) + 209]

= – 20 + 0 = – 20

6/ (– 12) + ( – 13) + 36 + (– 11)

= (– 25) + (– 11) + 36

= – 36 + 36 = 0

7/ 300 – (– 200) – (– 120) + 18

= 300 + 200 + 120 + 18

= 500 + 120 + 18

= 620 + 18

= 638

8/ – (– 299) + (– 219) – 401 + 12

= 299 – 219 – 401 + 12

= 80 – 401 + 12

= – 321 + 12 = – 309

9/ 555 – (– 333) – 100 – 80

= 555 + 333 – 180

= 888 – 180

= 708

10/ 34 + 35 + 36 + 37 – 14 – 15 – 16 – 17

= (34 – 14) + (35 – 15) + (36 – 16) + (37 – 17)

= 20 + 20 + 20 + 20

= 80

11/ 1+ (– 2) + 3 + (– 4) + ..... + 19 + (– 20)

=[1 + (– 2)] . [(20 – 1) : 1 + 1] : 2 = – 1 . 10 = – 10

12/ 1 – 2 + 3 – 4 + ... + 99 – 100

= (1 – 2) . [(100 – 1) : 1 + 1] : 2 = –1 . 50 = – 50

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