The total number of students who opted for Mathematics in the years 2005 and 2008 together is approximately what percent of the total number of students who opted for all three subjects in the same years?

Number of students opting Mathematics in 2005 and 2008
= 15000 + 30000
= 45000
Number of students opting for these three subjects in 2005 and 2008
= {(5 + 35 + 15) + (25 + 30 + 30)} thousands
= 55000 + 85000
= 140000
$$\eqalign{ & \text{Required %} \cr & = \left(\frac{45000}{140000}\times100\right)\% \cr & = \frac{225}{7}\% \cr & = 32.14\% \cr & \approx 32\% \cr} $$