Question

A section of a boardwalk is made using 15boards. Each board is 9/1/4 inches wide. The total width of the section is 144 inches. The spacing between each board is equal. What is the width of the spacing between each board.

Answer 1

If there are 15 boards there are 14 gaps in-between. 
But first, 15 boards each 9 and 1/4th inches so you get  a total of 138 inches and 3/4th
If you subtract that from 144 you get 5 inches and 1/4th. The remaining amount is the total of all of the distance from the spacing.
Then you divide that by 14 (number of gaps/spacing in-between.)
So you get .375 inches. (3/8)
So width of the spacing between each board is 3/8ths of a inch