What math operations are needed to solve a problem like this, and how do you solve it?:
One sign flashes every 4 seconds, and another sign flashes every 14 seconds. At a certain instant, the 2 signs flash at the same time. How many seconds elapse until the 2 signs next flash at the same time?
A. 9
B. 10
C. 18
D. 28
E. 56
One sign flashes every 4 seconds, and another sign flashes every 14 seconds. At a certain instant, the 2 signs flash at the same time. How many seconds elapse until the 2 signs next flash at the same time?
A. 9
B. 10
C. 18
D. 28
E. 56
1 Answer
Jun 23, 2017
D. 28
Explanation:
The period of the system of two lights will be the least common multiple (LCM) of the periods of the individual lights.
Looking at the prime factorisations of
#4 = 2*2#
#14 = 2*7#
The LCM is the smallest number that has all of these factors in at least the multiplicities in which they occur in each of the original numbers.
That is:
#2*2*7 = 28#
So the period of the system will be
