\frac{10 \sqrt40}{\sqrt5}

$$\small{\text{
$ \frac{10 \sqrt40}{\sqrt5} =10 \sqrt{ \frac {40} {5} }= 10\sqrt{8} = 10 \sqrt{4*2}= 10*2*\sqrt{2} = 20\sqrt{2} = 28.2842712475 $
}}$$

.

$$\dfrac{10\sqrt{40}}{\sqrt{5}}=\boxed{42.29485053762256}$$

.