`a)\sqrt{75}+\sqrt{48}-\sqrt{300}`
`=\sqrt{25.3}+\sqrt{16.3}-\sqrt{100.3}`
`=5\sqrt{3}+4\sqrt{3}-10\sqrt{3}`
`=-\sqrt{3}`
`b)2\sqrt{18}-3\sqrt{32}-3\sqrt{27}+\sqrt{50}`
`=2\sqrt{9.2}-3\sqrt{16.2}-3\sqrt{9.3}+\sqrt{25.2}`
`=6\sqrt{2}-12\sqrt{2}-9\sqrt{3}+5\sqrt{2}`
`=-\sqrt{2}-9\sqrt{3}`
`c)(5\sqrt{2}-2\sqrt{5}).\sqrt{5}-\sqrt{250}`
`=5\sqrt{10}-2.5-\sqrt{25.10}`
`=5\sqrt{10}-10-5\sqrt{10}`
`=-10`