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PostPosted: Fri Oct 11, 2013 7:32 pm 
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i hope someone can help with this maths question...i know the answer but need to know how it was worked out

Q.16

A red light flashes four times in a minute and a green light flashes 6 times a minute. If both lights start flashing at the same instant, how many times do they flash at the same instant in one hour including the first and the last time?

i've spent far to long trying to work it out , i'm sure its simple, but i just cant see it. :oops: :oops: somebody please help..

Thank You in advance


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PostPosted: Fri Oct 11, 2013 8:11 pm 
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mummyjee wrote:
i hope someone can help with this maths question...i have the answer but need to know how it was worked out

Q.16

A red light flashes four times in a minute and a green light flashes 6 times a minute. If both lights start flashing at the same instant, how many times do they flash at the same instant in one hour including the first and the last time?

i've spent far too long trying to work it out , i'm sure its simple, but i just cant see it. :oops: :oops: somebody please help..

Thank You in advance


well I suppose:
red flashes at
15s
30s
45s
60s

and green flashes at:
10s
20s
30s
40s
50s
60s


so I reckon they flas together at 30 and 60? or have I got that wrong :?


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PostPosted: Fri Oct 11, 2013 8:18 pm 
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Both flash twice per minute -at 30 & 60 seconds = 120 per hour . Plus the 2 flash together at the start. So total 122 ????!

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PostPosted: Fri Oct 11, 2013 8:28 pm 
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thank you both....answer is 121

dlb how did you get to 120?


Last edited by mummyjee on Fri Oct 11, 2013 8:30 pm, edited 1 time in total.

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PostPosted: Fri Oct 11, 2013 8:29 pm 
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depends of course if the second at the top of the hour is counted once or twice

ie does the hour start at 00.00 and finish at 00.59 in which case there will be 60*00s and 60*30s

if the second at the top of the hour is counted twice ie an hours is 00.00 to 01.00 then there will be 61 * 00s and 60*30s = 121


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PostPosted: Fri Oct 11, 2013 8:30 pm 
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They begin together :

Red 0, 15, 30, 45
Green 0, 10, 20, 30, 40, 50

So the same at 0 & 30.

60 x 2 = 120

Badly worded though as there would be a final flash at 60s of the final minute and make 121. But that would give 5 flashes per minute for red and 7 for green!


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PostPosted: Fri Oct 11, 2013 8:32 pm 
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121

As above... Co-incident flash on 00:30 and 01:00... and they start ON!

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PostPosted: Fri Oct 11, 2013 8:34 pm 
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Bobmumof3 wrote:
They begin together :

Red 0, 15, 30, 45
Green 0, 10, 20, 30, 40, 50

So the same at 0 & 30.

60 x 2 = 120

Badly worded though as there would be a final flash at 60s of the final minute and make 121. But that would give 5 flashes per minute for red and 7 for green!



this looks about right...thank you very much.


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PostPosted: Fri Oct 11, 2013 8:36 pm 
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Should be in Maths section :D

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PostPosted: Fri Oct 11, 2013 8:37 pm 
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SunlampVexesEel wrote:
121

As above... Co-incident flash on 00:30 and 01:00... and they start ON!



so they flash together on 30 and 60 plus first flash..rite?


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