What is the equivalent ratio to 5: 10

1/2
All you need to do is either multiply or divide the left side and the right side with the same number 

There are many. All answers are right as long as you multiply or divide both terms by the same number (and it can be any number). so if I choose 3, the equivalent ratio would be 15:30

72 is the mode because it shows up the most number of times