Предмет: Математика, автор: Аноним

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Ответы

Автор ответа: bbbapho
0

3. A

 \frac{4}{5}  \times (5 \frac{1}{4}  - 7 \frac{1}{3} ) -  \frac{5}{6}  = - 2 \frac{1}{2}

1) 5 \frac{1}{4}  -  7\frac{1}{3}  =  \frac{5 \times 4 + 1}{4}  -  \frac{7 \times 3 + 1}{3}  =  \frac{21}{4}  -  \frac{22}{3}  =  \frac{21 \times 3}{12}  -  \frac{22 \times 4}{12}  =  \frac{63}{12}  -  \frac{88}{12}  =  \frac{63 - 88}{12}  =  \frac{ - 25}{12}  =  -  \frac{25}{12}

2)  \frac{4}{5}  \times ( -  \frac{25}{12} ) =  -  \frac{4 \times 25}{5 \times 12}  = -   \frac{4 \times 5 \times 5}{5 \times 4 \times 3}  =  -  \frac{5}{3}

3)  - \frac{5}{3}  -  \frac{5}{6}  =  -  \frac{5 \times 2}{3 \times 2}  -  \frac{5}{6}  =  -  \frac{10}{6}  -  \frac{5}{6}  =  - ( \frac{10}{6}  +  \frac{5}{6} ) =  -  \frac{10 + 5}{6}  =  -  \frac{15}{6}  =  -  \frac{5}{2}  =  -  \frac{4 + 1}{2}  =  - 2 \frac{1}{2}

4. B

(2 +  \frac{1}{3} ) \times (188 \frac{3}{5}  - 185 \frac{3}{5} ) = 7

1) 2 +  \frac{1}{3}  = 2 \frac{1}{3}  =  \frac{2 \times 3 + 1}{3}  =  \frac{7}{3}

2) 188 \frac{3}{5}  - 185 \frac{3}{5}  = (188 +  \frac{3}{5} ) - (185 +  \frac{3}{5} ) = (188 - 185) + ( \frac{3}{5}  -  \frac{3}{5} ) = 3 + 0 = 3

3)  \frac{7}{3}  \times 3 =  \frac{7 \times 3}{3}  =  \frac{7}{1}  = 7

5. A

(15 \frac{4}{5}  - 9 \frac{3}{10} ) - (12 \frac{9}{10}  - 8 \frac{3}{5} ) = 2.2

1) 15 \frac{4}{5}  - 9 \frac{3}{10}  = (15 +  \frac{4}{5} ) - (9 +  \frac{3}{10} ) = (15 - 9) + ( \frac{4}{5}  -  \frac{3}{10} ) = 6 + ( \frac{8}{10}  -  \frac{3}{10} ) = 6 +  \frac{8 - 3}{10}  = 6 +  \frac{5}{10}  = 6 +  0.5 = 6.5

2) 12 \frac{9}{10}  - 8 \frac{3}{5}  = (12 +  \frac{9}{10} ) - (8 +  \frac{3}{5} ) = (12 - 8) + ( \frac{9}{10}  -  \frac{3}{5} ) = 4 + ( \frac{9}{10}  -  \frac{6}{10} ) = 4 +  \frac{9 - 6}{10}  = 4 +  \frac{3}{10}  = 4  + 0.3 = 4.3

3) 6.5 - 4.3 = 2.2

6. C

(13 \frac{7}{12}  - 8 \frac{1}{3} ) \times ( -  \frac{3}{7} ) = - 2.25

1) 13 \frac{7}{12}  - 8 \frac{1}{3}  = (13 +  \frac{7}{12} ) - (8 +  \frac{1}{3} ) = (13 - 8) + ( \frac{7}{12}  -  \frac{1}{3} ) = 5 +  (\frac{7}{12}  -  \frac{4}{12} ) = 5 +  \frac{7 - 4}{12}  = 5 +  \frac{3}{12}  = 5 +  \frac{1}{4}  = 5 \frac{1}{4}

2) 5 \frac{1}{4}  \times ( -  \frac{3}{7} ) =  \frac{21}{4}  \times ( -  \frac{3}{7} ) =  -  \frac{21 \times 3}{4 \times 7}  =  -  \frac{7 \times 3 \times 3}{4 \times 7}  =  -  \frac{9}{4}  =  - 2 \frac{1}{4}  =  - 2.25

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