Question

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

Options

• 7 and 1/2 seconds

• 7 seconds

• 7 and 1/2 minutes

• 7 minutes

Answer 1

7 and 1/2 seconds

Explanation:

Time required to complete one revolutio0n of each wheel is `1/4,1/24,1/26` minute respectively.

`1/40 "min" = 60/40  "sec" =3/2"sec".`

`1/24 "min" = 60/24 "sec" = 5/2 "sec".`

`1/16 "min" - 60/16 "sec" = 15/4."sec".`

Now, L.C.M. of `3/2,5/2` and `15/4`

`=("L.C.M. of 3, 5, 15")/("H.C.F. of 2, 2, 4")=15/2 "sec". =7 1/2 "sec".`