A Light Blink After Every 3 Seconds, Another Light Blinks After Every 5 Seconds. How many Times do they Blink Together in half an hour?

Answer: 

We need to find how frequently do they flicker together in thirty minutes.

As indicated by the given subtleties

We take the LCM of 3 and 5

i.e, LCM (3,5) = 15

1 hour = an hour = 3600 seconds

1/2 hr = 3600/2sec

= 1800sec

Number of times they flicker together

Times in 30 mins= 1800/15 = 120

Thus, both the lights flicker multiple times in the given time of thirty minutes.