jamesk486 wrote:A certain clock marks every hour by striking a # of times equal to the hour, and the time required for a stroke is exactly equal to the time interval between the strokes. At 6:00, the time lapse between the beginning of the first stroke and the end of the last stroke is 22 seconds. At 12:00, how many seconds elapse between the beginning of the first stroke and the end of the last stroke?

A:72
B:50
C:48
D:46
E:44

The answer explanation is so obscure that I don't know what they're talking about!

let the time for a stroke be x ... let the timer between the stroke be y .. now at 6 .. the clock will strike 6 times and the no of intervals between the strokes is 5 . so the total time will be x+y+x+y+x+y+x+y+x+y+x = 6*x + 5*y .. but x = y .. so the total time is 11*x =22 .. so x = 2..

therefore, the time for a stroke = the interval between the stroke = 2 seconds ...

at 12 .. the no of times the clock will strike is 12 and the no of intervals between the stroke is 11 .. therfore the total = (12+11)*x= 23*2 = 46 seconds .. now the q asks for the time elapsecd after the first stroke and the last stroke .. the first stroke will take 2 seconds .. so the time elapsed = total - 2 = 46-2 =44 seconds.. so the answer is E ... hope it helps..

Thanks Gabriel...Pretty obscure question!

yes, thank you! i definitely understand now~

gabriel wrote: let the time for a stroke be x ... let the timer between the stroke be y .. now at 6 .. the clock will strike 6 times and the no of intervals between the strokes is 5 . so the total time will be x+y+x+y+x+y+x+y+x+y+x = 6*x + 5*y .. but x = y .. so the total time is 11*x =22 .. so x = 2..

therefore, the time for a stroke = the interval between the stroke = 2 seconds ...

at 12 .. the no of times the clock will strike is 12 and the no of intervals between the stroke is 11 .. therfore the total = (12+11)*x= 23*2 = 46 seconds .. now the q asks for the time elapsecd after the first stroke and the last stroke .. the first stroke will take 2 seconds .. so the time elapsed = total - 2 = 46-2 =44 seconds.. so the answer is E ... hope it helps..

Thank you for the explanation, Gabriel! It really helped me understand where did "11" come from. For the record, the official answer is D: 46 seconds. I think subtracting 2 seconds for the first stroke is unnecessary since the q did ask "between the beginning of the first stroke and...".

At 6>>>>strike-pause,strike-pause,strike-pause,strike-pause,strike-pause,strike
so 11x=22
therefor x=2
At 12>>>> 23x
therefor, 23*2=46
so Answer is D