2021-08-18

Dare2solve | Ratio of areas formed due to random point on square to area of square

This question was uploaded on my Instagram, Facebook and Twitter account on 17th of August 2021. You can check it on my Social media account. Kindly follow my accounts for daily new puzzles. You will get daily one puzzle at 4.00 UTC (Convert it as per your country timing).

All vertices of square are joined with a common random point inside square. Find ratio of sum of areas of triangles formed either sides of that point (Upper + Lower or Left + Right) to area of square. 

Give this question a try then check your answer with solution.

(Shortcut Image Solution with Calculations is gives below in this post)

Solution 1:

Step 1:
Draw a perpendicular line on upper and lower side passing through that point.
Let side of square be x.
Step 2:
Let height of upper triangle be x,
⇒ Height of lower triangle be (x - a)

⇒ Area of upper triangle be ax / 2
⇒ Area of lower triangle be (x - a)x / 2

⇒ Sum of Blue area be (a + (x - a))x / 2 = x² / 2

Also area of square = x²

Step 3:
Ratio of areas = x² / 2  :  x²  =  1 : 2


Image solution:



Solution 2:
Step 1:
Draw a perpendicular line on upper and lower side passing through that point.
Draw a perpendicular line on left and right side passing through that point.
Step 2:
Now you can observe 4 pairs of similar triangles.
Let their areas are a1, a2, a3, a4.

Blue area = a1 + a2 + a3 + a4 = A
Square area = 2(a1 + a2 + a3 + a4) = 2A
Step 3:
Ratio of areas = A : 2A  =  1 : 2


Image solution:








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