tricky question. help needed please!

[mummyjee]

Should be in Maths section

i posted it in both this section and maths. this section seems to have more activity at the mo .. and i needed the answer quick, otherwise couldnt sleep!!!

[Bobmumof3]

Nothing like some Friday night maths to stop me thinking about the morning post!

[aliportico]

Ok, so when will they flash in the first minute?

Red flashes 4 times in a minute - so if it starts flashing at 0s, it then flashes again at 15s, 30s, 45s and 60s.

Green flashes 6 times, so if it starts at 0s, it also flashes at 10, 20, 30, 40, 50 and 60s.

So they start flashing at the same time, and then flash simultaneously twice more in each minute.

Count the first double flash, then 2 x 60 for the hour = 121.

[dlb]

Err! Oops! I said 120 plus 2 - should have said 120 plus 1 when both flash at start not plus 2 when both flash at start! Good job I'm not 11.....

[mummyjee]

Ok, so when will they flash in the first minute?

Red flashes 4 times in a minute - so if it starts flashing at 0s, it then flashes again at 15s, 30s, 45s and 60s.

Green flashes 6 times, so if it starts at 0s, it also flashes at 10, 20, 30, 40, 50 and 60s.

So they start flashing at the same time, and then flash simultaneously twice more in each minute.

Count the first double flash, then 2 x 60 for the hour = 121.

Thank you very much - this is correct. thank goodness for this forum! i totally misunderstood the question myself!