Question

A person is to install five devices each 6 7/8 inches wide with 3 1/2 inches between switches. how much space will be needed to mount these switches?

Answer 1

Refer to the diagram shown below.

w = 6 7/8 in = 6.875 in, the width of each device.
d = 3 1/2 in = 3.50 in, the space between teo devices.

The total space needed is
D = 4(w+d) + w
    = 5w + 4d
    = 5*6875 + 4*3.5 
D  = 48.375 in  or 48 3/8 in

Answer:  48 3/8 inches or 48.375 inches