The given Bar graph presents the number of students from Science and Arts streams from a school in different years.

What is the ratio of the total number of Science students in 2011 and 2015 to that of Arts in 2012 and 2015 ?

As shown in the bar graph science students indicated with blue color and Arts students indicated with dark brown color

Total number of science students in 2011 and 2015 from the question is=(225+375) = 600

Total number of arts students in 2012 and 2015 is =(325+325) = 650

Hence Required Ratio= $$\frac{600}{650}\ =\ \frac{12}{13}$$ 

Hence the ratio of the total number of science and arts students is =12:13