A ratio between two numbers is 3 : 4 and their L.C.M. is 84. The first number is	Options:  A) 60  B) 45  C) 21  D) 15  E) None
Sol.   Let the required numbers be 3x and 4x. Then, their L.C.M. is 12x.   ∴ 12x = 84⇔ x = 7. Hence, the first number is 21.   Answer 21
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A ratio between two numbers is 3 : 4 and their L.C.M. is 84. The first number is