Please help me with a SURDS question (C1)

Please show me how to simplify the following:

(2+√5)(5-√20)

expand the brackets:
10-2√20+5√5-10
simplify:
10-10-2√20+5√5
-2√20+5√5
breakdown √20 into √4√5 then 2√5
-2(2√5)+5√5
-4√5+5√5
and therefore the answer is √5
hope thats right!

Hi,

(2+√5)(5-√20) =

10 - 2√20 + 5√5 - √100 =

10 - 4√5 + 5√5 - 10 = √5 <==ANSWER

I hope that helps!! :-)

(2 + √5)(5 - √20)

= (2+√5)(5 - √(4*5))

= (2 + √5)(5 - 2√5 )

= 10 - 4√5 + 5√5 - 10

= √5

(2+√5)(5-√20)
= 10-2√20+5√5-√100
= 10-4√5+5√5-10
= -4√5+5√5
=√5