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Tricky Maths Question- help needed please
Posted: Fri Oct 11, 2013 8:32 pm
by mummyjee
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.
somebody please help..
Thank You in advance
Re: tricky question. help needed please!
Posted: Fri Oct 11, 2013 9:11 pm
by hermanmunster
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.
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
Re: tricky question. help needed please!
Posted: Fri Oct 11, 2013 9:18 pm
by dlb
Both flash twice per minute -at 30 & 60 seconds = 120 per hour . Plus the 2 flash together at the start. So total 122 ????!
Re: tricky question. help needed please!
Posted: Fri Oct 11, 2013 9:28 pm
by mummyjee
thank you both....answer is 121
dlb how did you get to 120?
Re: tricky question. help needed please!
Posted: Fri Oct 11, 2013 9:29 pm
by hermanmunster
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
Re: tricky question. help needed please!
Posted: Fri Oct 11, 2013 9:30 pm
by Bobmumof3
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!
Re: tricky question. help needed please!
Posted: Fri Oct 11, 2013 9:32 pm
by SunlampVexesEel
121
As above... Co-incident flash on 00:30 and 01:00... and they start ON!
Re: tricky question. help needed please!
Posted: Fri Oct 11, 2013 9:34 pm
by mummyjee
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.
Re: tricky question. help needed please!
Posted: Fri Oct 11, 2013 9:36 pm
by SunlampVexesEel
Should be in Maths section
Re: tricky question. help needed please!
Posted: Fri Oct 11, 2013 9:37 pm
by mummyjee
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?