Answer: The part of the stock owned by neither Rob nor Talia is
13/16
Explanation:
Let the total stock in the local bread company be represented by x
Rob owns 1/8 of the stock in the local bread company. This means that the amount of stock owned by Rob is 1/8 × x = x/8
His sister Talia owns half as much stock as Rob. This means that the amount of stock owned by Talia would be 1/2 × x/8 = x/16
Total part of the stock owned by Talia and Rob would be
x/8 + x/16 = (2x+x)/16 = 3x/16
The part of the stock owned by neither Rob nor Talia will be the total stock minus the part of the stock owned by Rob and Talia.
It becomes
x - 3x/16 = (16x - 3x)/16 = 13x/16