If a square mirror has a 20-inch

Cameron Layer

Here is another easy way to do it. :)
The diagonal of a square is side (S) times √2. √2 is approx 1.4
(diagonal = s√2)

Therefore
20 = S√2
20 ≈ S√1.4
20/1.4 ≈ S
S ≈ 14.5
4S ≈ 58
Answer choice B.

Sep 22, 2020 • Comment

Nathaniel Gooden

It is simply two 3:4:5 triangles. If you divide the square into two triangles and make similar triangles then you can compare. The diagonal is 20 which is 5 x "4". Multiply "4" to the 3 and 4 on the 3:4:5 triangle to get 12:16:20. Now you have the sides of one half of the square. That being 12 and 16. Add them up:
12
12
16
16
=56, which is approximate to 60....Answer Choice B.

Dec 20, 2017 • Comment

Let´s start with one of the two 45 -45 - 90 triangles.

It follows a proportion of: x - x - x * (root of 2) (opposite sides of the angles).

Since 20 is the hypotenuse, 20 = x * (root of 2)

So, x = (20 / (root of 2) )

If the perimeter = 4x,

4x = 4 * (20 / (root of 2) ) = (80 / (root of 2) )

Multiply numerator and denominator by root of 2:

(80 * (root of 2)) / ((root of 2) * (root of 2))

(80 * (root of 2)) / 2

(40* (root of 2)) = 57 prox.

Correct answer = 60.

Jan 26, 2015 • Comment

Mike McGarry, Magoosh Tutor

Dec 28, 2013 • Comment