In the diagram shown, 21 identical plastic balls were placed between two walls with equally spaced gaps between them. The first plastic ball and the last plastic ball were touching the front wall and last wall respectively. Given that the distance between the two walls was 431 m and that the radius of a plastic ball was 5 m. Find the length of the gap between any two adjacent plastic balls as shown.
Diameter of the plastic ball
= 5 x 2 
= 10 m

Distance covered by 21 balls
= 21 x 10
= 210 m

Distance left for the gaps
= 431 - 210
= 221 m

Total number of gaps between the balls
= 21 - 1
= 20

Length of the gap between two balls
= 221 ÷ 20
= 11.05 m

Answer(s): 11.05 m