The given bar graph shows the data of the number of students who were called for an interview by a company 'XYZ' from three different institutes A, B and C over the years. Study the bar graph and answer the question.
What is the ratio of the average number of students called for an interview from institute C in the period 2018 to 2020 to the average number of students called for an interview from institute B in the same period?
1
1 ∶ 3
2
13 ∶ 12
3
12 ∶ 13
4
14 ∶ 15