Solution:
According to the problem, we have that:
Santa ate 3/7 of candies
and
Mrs. Claus ate 2/7 of the same candies.
Then the total part of the candies consumed by both is:
[tex]\frac{3}{7}+\frac{2}{7}=\frac{5}{7}[/tex]this means that both have consumed 5/7 of the total candies.
So that, we can conclude that the correct answer is:
[tex]\frac{5}{7}[/tex]