Posted by **chelsea** on Sunday, September 26, 2010 at 4:38am.

a light house flashes every 56 seconds. Another lighthouse flashes every 40 seconds. At 9 p.m. they both flash t the same time. What time will it e when they next both flash at the same time?

- maths -
**Reiny**, Sunday, September 26, 2010 at 7:04am
first lighthouse will flash in 56 sec, then 112, 168 , etc seconds

second lighthouse will flash in 49 sec, then 80, 120, etc seconds

so this is just like finding the LCD of 56 and 40

56 = 2x2x2x7

40 = 2x2x2x5

LCD = 2x2x2x5x7 = 280

so they will flash together 280 seconds from now or 4 minutes and 40 seconds from 9 pm

which would be 9:04:40 pm

## Answer this Question

## Related Questions

- Math - Three lighthouses on three nearby islands flash their lights every ...
- MATH - One light flashes every 2 minutes and another light flashes every 3.5 ...
- MATH - One light flashes every 2 minutes and another light flashes every 3.5 ...
- Mathh :/ - A light flashes every 15 minutes. a second light flashes every 18 ...
- Math - the green light flashes every 3 seconds,the red every 5 seconds and white...
- general ability - light X flashes every 3 minutes. Light Y flashes every 5 ...
- tech III math ( ACT Prep) - A neon sign flashes every 4 seconds, another neon ...
- physics - A law enforcement officer in an intergalactic "police car" turns on a ...
- Physics - A stroboscope is a light that flashes on and off at a constant rate. ...
- math - The manager turns the restaurants two neon signs on at the same time both...