# Thread: Ratio and proportion 2

1. ## Ratio and proportion 2

Hello!
This is a question about ratio and proportion.

When I solve the question I get the answer to be sqrt21, which isn't correct. The correct answer is a).
Thanks,
Amine.

Hello!
This is a question about ratio and proportion.

When I solve the question I get the answer to be sqrt21, which isn't correct. The correct answer is a).
Thanks,
Amine.
HI

$a+b=\sqrt{(1-\sqrt{5})^2}+\sqrt{(\sqrt{5}-\sqrt{20})^2}$

$=|1-\sqrt{5}|+|\sqrt{5}-\sqrt{20}|$

$=|1-\sqrt{5}+\sqrt{5}-\sqrt{20}|$

$=|1-\sqrt{20}|$

$=1-\sqrt{20}$ or $\sqrt{20}-1$

Since it must be positive , then take $\sqrt{20}-1$