Question

The manager turns on the restaurants two neon lights at the same time both signs blink as they are turned on one sign blinks every nine seconds the other side and blinks every 15 seconds in how many seconds will they blink together again

Answer 1

We use the multiples of 9 and 15.
9:9,18,27,36,45,54,63,73,81,90,99,108,117,126,135
15:15,30,45,60,75,90,105,120,135
The first common multiple in this case it is 135 is the answer as they asked in how many secnds the two neon lights blink together again