If you count 20 seconds between seeing lightning and hearing the thunder, how far is the storm away from you?
Official USCG Answer & Rule Citation
Correct Answer: Option B — 4 miles
Sound travels through the atmosphere at approximately 1 mile every 5 seconds. Dividing the measured 20-second interval between the flash of lightning and the sound of thunder by 5 yields a direct distance of 4 miles from the storm.
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