Three numbers are in the ratio 3:4:5 and their L.C.M is 2400. Their H.C.F is:

A. 40
B. 80
C. 120
D. 200
Let the numbers be 3x, 4x and 5x.
Then, their L.C.M = 60x. So, 60x = 2400 or x = 40.
The numbers are (3 * 40), (4 * 40) and (5 * 40).
Hence, required H.C.F = 40.