$\sqrt{36\ast 81}=\sqrt{36}\ast \sqrt{81}=6\ast 9=54$

$\sqrt{900\ast 49}=\sqrt{900}\ast \sqrt{49}=30\ast 7=210$

$\sqrt{16\ast 0,25}=\sqrt{16}\ast \sqrt{0,25}=4\ast 0,5=2$

$\sqrt{9\ast 1,69}=\sqrt{9}\ast \sqrt{1,69}=3\ast 1,3=3,9$

$\sqrt{0,36\ast 1,21}=\sqrt{0,36}\ast \sqrt{1,21}=0,6\ast 1,1=0,66$

$\sqrt{5^2\ast 3^6}=\sqrt{5^2}\ast \sqrt{3^6}=\sqrt{5^2}\ast \sqrt{(3^3{)}^2}=|5|\ast |3^3|=5\ast |27|=5\ast 27=135$

$\sqrt{4^4\ast 3^2}=\sqrt{4^4}\ast \sqrt{3^2}=\sqrt{(4^2{)}^2}\ast \sqrt{3^2}=|4^2|\ast |3|=|16|\ast 3=16\ast 3=48$

$\sqrt{2^6\ast 5^2}=\sqrt{2^6}\ast \sqrt{5^2}=\sqrt{(2^3{)}^2}\ast \sqrt{5^2}=|2^3|\ast |5|=|8|\ast 5=8\ast 5=40$

$\sqrt{2,25\ast 0,04\ast 1600}=\sqrt{2,25}\ast \sqrt{0,04}\ast \sqrt{1600}=1,5\ast 0,2\ast 40=0,3\ast 40=12$

$\sqrt{13\frac{4}{9}}=\sqrt{\frac{121}{9}}=\frac{\sqrt{121}}{\sqrt{9}}=\frac{11}{3}=3\frac{2}{3}$

$\sqrt{1\frac{7}{9}\ast \frac{4}{25}}=\sqrt{\frac{16}{9}}\ast \sqrt{\frac{4}{25}}=\frac{\sqrt{16}}{\sqrt{9}}\ast \frac{\sqrt{4}}{\sqrt{25}}=\frac{4}{3}\ast \frac{2}{5}=\frac{8}{15}$

$\sqrt{\frac{1}{16}\ast \frac{9}{25}}=\sqrt{\frac{1}{16}}\ast \sqrt{\frac{9}{25}}=\frac{\sqrt{1}}{\sqrt{16}}\ast \frac{\sqrt{9}}{\sqrt{25}}=\frac{1}{4}\ast \frac{3}{5}=\frac{3}{20}$