If you hear thunder 36 seconds after you see a flash of lightning how far away is the thunderstorm?

About 12 kilometers (7.45 miles). After you see a bolt of lightning, for every 3 seconds until you hear the thunder, it means it is one kilometer away (3 seconds = 1 kilometer). This is because the sound wave created by the lightning is traveling at about 330 m/sec (in dry air, the speed of sound is about 343 m/sec or 1127 ft/sec).

You can also divide by 5 to determine the approximate number of miles. In this case it would be calculated as about 7.2 miles away.