A ratio between two numbers is 3 : 4 and their L.C.M. is 180. The first number is	Choose one:
A) 60 B) 45 C) 20 D) 15 E) none

Rationale: "sol . let the required numbers be 3 x and 4 x . then , their l . c . m . is 12 x . ∴ 12 x = 180 ⇔ x = 15 . hence , the first number is 45 . answer b"
Answer: B