Hướng dẫn Giải Bài 3.18 (Trang 71, SGK Toán 6, Tập 1, Bộ Kết Nối Tri Thức)

Thay mỗi dấu “*” bằng một chữ số thích hợp để có: <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>)</mo><mo> </mo><mfenced><mover><mrow><mo>-</mo><mn>6</mn><mo>*</mo></mrow><mo>¯</mo></mover></mfenced><mo>+</mo><mfenced><mrow><mo>-</mo><mn>34</mn></mrow></mfenced><mo>=</mo><mo>-</mo><mn>100</mn><mo>;</mo></math> <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>b</mi><mo>)</mo><mo> </mo><mfenced><mrow><mo>-</mo><mn>789</mn></mrow></mfenced><mo>+</mo><mover><mrow><mn>2</mn><mo>*</mo><mo>*</mo></mrow><mo>¯</mo></mover><mo>=</mo><mo>-</mo><mn>515</mn><mo>;</mo></math> Giải: <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>)</mo><mo> </mo><mfenced><mover><mrow><mo>-</mo><mn>6</mn><mo>*</mo></mrow><mo>¯</mo></mover></mfenced><mo>+</mo><mfenced><mrow><mo>-</mo><mn>34</mn></mrow></mfenced><mo>=</mo><mo>-</mo><mn>100</mn><mo>;</mo><mspace linebreak="newline"/><mover><mrow><mo>-</mo><mn>6</mn><mo>*</mo></mrow><mo>¯</mo></mover><mo>=</mo><mo>-</mo><mn>100</mn><mo>-</mo><mfenced><mrow><mo>-</mo><mn>34</mn></mrow></mfenced><mspace linebreak="newline"/><mover><mrow><mo>-</mo><mn>6</mn><mo>*</mo></mrow><mo>¯</mo></mover><mo>=</mo><mo>-</mo><mn>100</mn><mo>+</mo><mn>34</mn><mspace linebreak="newline"/><mover><mrow><mo>-</mo><mn>6</mn><mo>*</mo></mrow><mo>¯</mo></mover><mo>=</mo><mo>-</mo><mfenced><mrow><mn>100</mn><mo>-</mo><mn>34</mn></mrow></mfenced><mspace linebreak="newline"/><mover><mrow><mo>-</mo><mn>6</mn><mo>*</mo></mrow><mo>¯</mo></mover><mo>=</mo><mo>-</mo><mn>66</mn></math> Vậy dấu * là chữ số 6. <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>b</mi><mo>)</mo><mo> </mo><mfenced><mrow><mo>-</mo><mn>789</mn></mrow></mfenced><mo>+</mo><mover><mrow><mn>2</mn><mo>*</mo><mo>*</mo></mrow><mo>¯</mo></mover><mo>=</mo><mo>-</mo><mn>515</mn><mspace linebreak="newline"/><mover><mrow><mn>2</mn><mo>*</mo><mo>*</mo></mrow><mo>¯</mo></mover><mo>=</mo><mo>-</mo><mn>515</mn><mo>-</mo><mfenced><mrow><mo>-</mo><mn>789</mn></mrow></mfenced><mspace linebreak="newline"/><mover><mrow><mn>2</mn><mo>*</mo><mo>*</mo></mrow><mo>¯</mo></mover><mo>=</mo><mo>-</mo><mn>515</mn><mo>+</mo><mn>789</mn><mspace linebreak="newline"/><mover><mrow><mn>2</mn><mo>*</mo><mo>*</mo></mrow><mo>¯</mo></mover><mo>=</mo><mn>789</mn><mo>-</mo><mn>515</mn><mspace linebreak="newline"/><mover><mrow><mn>2</mn><mo>*</mo><mo>*</mo></mrow><mo>¯</mo></mover><mo>=</mo><mn>274</mn></math> Vậy hai dấu * lần lượt theo thứ tự từ trái qua phải là 7 và 4.