Question 1020583
Let x = # of days passed.
At x = 0, the amount remaining is 16 kg.
At x = 1, the amount remaining is {{{16 - (2/3)16 = 16*(1/3)}}} kg
At x = 2, the amount remaining is {{{16*(1/3) - (2/3)16*(1/3) = 16*(1/3)^2}}} kg
At x = 3, the amount remaining is {{{16*(1/3)^2 - (2/3)16*(1/3)^2 = 16*(1/3)^3}}} kg

By induction it follows that

{{{A(x) = 16/3^x}}}

if we let A(X) be the amount of dog food remaining after x days.