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