If the fuse burn rate is 40 seconds per foot, how long would a 5-foot fuse burn?

• A. 200 seconds
• B. 5 seconds
• C. 40 seconds
• D. 600 seconds

Answer: (A)

Burn time scales with length when the burn rate is constant. If a fuse burns for 40 seconds per foot, then a 5‑foot fuse will take 5 times as long as a 1‑foot piece. 5 × 40 = 200 seconds, so the fuse would burn for 200 seconds (about 3 minutes 20 seconds). The other numbers don’t fit because they correspond to different lengths: 5 seconds would be for a very short length, 40 seconds for one foot, and 600 seconds would require about 15 feet.