The answer is C. 4√5
To calculate this, we must find the greatest common divisor of these 3 numbers √20,√45, and √5.
The greatest common divisor is √5:
[tex] \sqrt{20} = \sqrt{5*4} = \sqrt{5} * \sqrt{4} = \sqrt{5} *2= 2\sqrt{5}[/tex]
[tex] \sqrt{45} = \sqrt{5*9} = \sqrt{5} * \sqrt{9}=\sqrt{5}*3 = 3\sqrt{5} [/tex]
Therefore,
[tex] \sqrt{20} + \sqrt{45}- \sqrt{5}=2 \sqrt{5} +3\sqrt{5}-1\sqrt{5}=\sqrt{5}(2+3-1)=4\sqrt{5}[/tex]
