A ratio between two numbers is 5:4 and their L.C.M. is 80. The first number is
Choose the correct choice from the following choices: A) 60 B) 45 C) 20 D) 15 E) none

Rationale: "sol . let the required numbers be 5 x and 4 x . then , their l . c . m . is 20 x . ∴ 20 x = 80 ⇔ x = 4 . hence , the first number is 20 . answer c"
Answer: C