In a school, the ratio of the number of large classrooms to small classrooms is 3:4. If the number of small rooms is 20, then find the number of large rooms.

Ratio of number of large classrooms to small classrooms = 3:4

Number of small classrooms = 20

⇒ ratio = =

⇒ =

Cross multiply we get

⇒ Number of large classrooms = = 3 × 10

Therefore, number of large classrooms is 30