78. Найдите значение выражения: a) 2/5 m, если m = 1/2; 2/5; 2 1/2; 1 7/8; 15/16;

а) 2/5 m, если m = 1/2; 2/5; 2 1/2; 1 7/8; 15/16;

• m = 1/2;
  2/5 · 1/2 = (2·1)/(5·2) = 1/5
• m = 2/5;
  2/5 · 2/5 = (2·2)/(5·5) = 4/25
• m = 2 1/2 = 5/2;
  2/5 · 5/2 = (2·5)/(5·2) = 1
• m = 1 7/8 = 15/8;
  2/5 · 15/8 = (2·15)/(5·8) = (2·3·5)/(5·4·2) = 3/4
• m = 15/16;
  2/5 · 15/16 = (2·15)/(5·16) = (2·3·5)/(5·8·2) = 3/8

Ответ: 1/5, 4/25, 1, 3/4, 3/8