If a square mirror has a 20-inch diagonal, what is the approximate perimeter R of the mirror, in inches?  Pick:	A) 40	B) 60	C) 80	D) 100	E) 120
if you draw the square and diagonal inside the square. u can see square becomes part of two triangles opposite to each other.   And We know the property of the triangle, addition of two sides of triangle must be greater than its diagonal in order to complete the triangle. And each side must be less than 20 and perimeter R must be less than 80, so we can eliminate answer choice C, D and E.   so Side 1 + side 2 &gt; 20, that means Side 1 or Side 2 must be &gt; 10. so we can eliminate the answer choice A.   Now we are left with is 60
<result>B</result>
If a square mirror has a 20-inch diagonal, what is the approximate perimeter R of the mirror, in inches?