A ratio between two numbers is 4:5 and their L.C.M. is 200. The first number is	Choices:
A) 60 B) 40 C) 20 D) 15 E) none

Rationale: "sol . let the required numbers be 4 x and 5 x . then , their l . c . m . is 20 x . ∴ 20 x = 200 ⇔ x = 10 . hence , the first number is 40 . answer b"
Answer: B