ABC26GN0570 · H.C.F. and L.C.M. of Numbers

Subject: General Aptitude · Chapter: H.C.F. and L.C.M. of Numbers · Exam: · Marks: · Difficulty:

Three wheels can complete 40, 24 and 16 revolutions per minute respectively. There is a red spot on each wheel that touches the ground at time zero. After how much time, all these spots will simultaneously touch the ground again? 61 1

(a)7 sec

(b)18 sec 2 1

(c)7 min

(d)18 min 2

Answer

Answer (as printed): A

Explanation

For one complete revolution, the first, second and third 60 60 60 3 5 15 wheels take , , seconds i.e., , , seconds 40 24 16 2 2 4 respectively. \ Time taken for all red spots to touch the ground again simultaneously.  3 5 15   L.C.M.of 3, 5, 15  =  L.C.M. of , ,  sec =  sec 2 2 4  H.C.F. of 2, 2, 4  15 1 = sec = 7 sec. 2 2 3

Explanation as extracted from the printed page; notation may be imperfect.

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