Madeline and Rufus are dogs and they are never indoors or outdoors at the same time.?

[Francine]

Yesterday, Madeline spent 2/3 of the day indoors. How long did Rufus spend indoors? (Hint: they do this 24 hours a day).

 

[Mermaid]

If they are never in the same place (indoors or outdoors) at the same time, then there must always be 1 dog in each place. Thus, the amount of time M spent inside + the amount of time R spent inside = 24 hours. OR, the fraction of the day M spent inside + the fraction R spent inside = 1.

So, 2/3 + (Rufus, inside) = 1.

1 - 2/3 = 1/3

Rufus spent 1/3 of the day indoors. 1/3 of 24 hours is 8 hours.