$A = \sqrt{8} + 10\sqrt{\dfrac{1}{2}} - \sqrt{50} = \sqrt{4.2} + 10\sqrt{\dfrac{2}{2^2}} - \sqrt{25.2}$
$= 2\sqrt{2} + \dfrac{10}{2}\sqrt{2} - 5\sqrt{2} = 2\sqrt{2} + 5\sqrt{2} - 5\sqrt{2} = 2\sqrt{2}$
$B = \sqrt{40} + 4\sqrt{\dfrac{5}{2}} - 5\sqrt{\dfrac{2}{5}}$
$B = \sqrt{4.10} + 4.\sqrt{\dfrac{5.2}{2.2}} - 5\sqrt{\dfrac{2.5}{5.5}}$
$B = 2\sqrt{10} + 2\sqrt{10} - \sqrt{10} = 3\sqrt{10}$
