1. Вычислите: а) 5 - 2/5; б) 9 3/4 - 6 5/12; в) 12 8/5 - 3; г) 9 3/4 + 2 11/25; д) 8 3/7 - 3 1/3; е) 12 1/9 - 1 3/5. B-3

Решение:

1. а) 5 - 2/5

\( 5 - \frac{2}{5} = \frac{25}{5} - \frac{2}{5} = \frac{23}{5} = 4 \frac{3}{5} \)

2. б) 9 3/4 - 6 5/12

\( 9 \frac{3}{4} - 6 \frac{5}{12} = 9 \frac{9}{12} - 6 \frac{5}{12} = (9 - 6) + (\frac{9}{12} - \frac{5}{12}) = 3 \frac{4}{12} = 3 \frac{1}{3} \)

3. в) 12 8/5 - 3

\( 12 \frac{8}{5} - 3 = 12 \frac{8}{5} - 3 \frac{0}{5} = (12 - 3) + (\frac{8}{5} - \frac{0}{5}) = 9 \frac{8}{5} = 10 \frac{3}{5} \)

4. г) 9 3/4 + 2 11/25

\( 9 \frac{3}{4} + 2 \frac{11}{25} = 9 \frac{75}{100} + 2 \frac{44}{100} = (9 + 2) + (\frac{75}{100} + \frac{44}{100}) = 11 \frac{119}{100} = 12 \frac{19}{100} \)

5. д) 8 3/7 - 3 1/3

\( 8 \frac{3}{7} - 3 \frac{1}{3} = 8 \frac{9}{21} - 3 \frac{7}{21} = (8 - 3) + (\frac{9}{21} - \frac{7}{21}) = 5 \frac{2}{21} \)

6. е) 12 1/9 - 1 3/5

\( 12 \frac{1}{9} - 1 \frac{3}{5} = 12 \frac{5}{45} - 1 \frac{27}{45} = 11 \frac{50}{45} - 1 \frac{27}{45} = (11 - 1) + (\frac{50}{45} - \frac{27}{45}) = 10 \frac{23}{45} \)

Ответ: а) 4 3/5; б) 3 1/3; в) 10 3/5; г) 12 19/100; д) 5 2/21; е) 10 23/45.