<PRE><B>Question 1119481</B>
A certain machine is composed of three led light blink in varied materials . The red light blinks every 8 seconds; the blue light blinks every 12 seconds; and the yellow light blinks every 18 seconds. If all lights blink together at exactly 3pm how many times will they blink again altogether until 3:30pm?
----
Find the least common multiple of 8,12, and 18.
8 = 2^3
12 = 2^2*3
18 = 2*3^2
----
The lcm has each prime factor in its highdest power
lcm = 2^3*3^2 = 8*9 = 72
---
All lights will blink at 3pm, 3pm+72sec, 3pm+2*72sec, etc
---
# of seconds in 30 min = 30*60 = 1800
1800/72 = 25
Ans:: 25 times
-----------------
Cheers,
Stan H.
----------- </PRE>