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