UPSC CDS Math Ratio Proportion and Variation Questions

Ratio of number of boys in first and second standards =2:3=8:12
Ratio of number of boys in second and third standards =4:5=12:15
Therefore, ratio of numbers in first, second and third standards =8:12:15
Number of boys in the first standard=(

8

8+12+15

)×350
=

8

35

×350=80
Number of boys in the third standard=(

15

8+12+15

)×350
=

15

35

×350=150
Therefore, total number of boys in the first and third standards =80+15=230