Ответ:

  1. \(0.4\sqrt{6400}=0.4\cdot80=32\).
  2. \(100\sqrt{0.16}-\frac{1}{26}\sqrt{169}=100\cdot0.4-\frac{13}{26}=40-0.5=39.5\).
  3. \(\frac{2}{9}\sqrt{5\frac{1}{16}}=\frac{2}{9}\sqrt{\frac{81}{16}}=\frac{2}{9}\cdot\frac{9}{4}=\frac{1}{2}\).
  4. \(\sqrt{784}-10\sqrt{2.56}=28-10\cdot1.6=12\).
  5. \(2.5\sqrt{3.24}-\frac12\sqrt{225}=2.5\cdot1.8-\frac12\cdot15=4.5-7.5=-3\).
  6. \(4-\frac14\sqrt{5\frac{11}{49}}=4-\frac14\sqrt{\frac{256}{49}}=4-\frac14\cdot\frac{16}{7}=4-\frac47=\frac{24}{7}\).

Ответ: 1) 32; 2) 39,5; 3) \(\frac12\); 4) 12; 5) −3; 6) \(\frac{24}{7}\).