MediumBrain Teasers

Burning Ropes — 45 Minutes

Goldman SachsMorgan Stanley

You have two ropes; each takes exactly 60 minutes to burn end-to-end, but neither burns at a uniform rate. With only a lighter, how do you measure exactly 45 minutes?

Approach

Burning a rope from both ends halves its time — regardless of unevenness.

Use the moment the first rope finishes as a trigger.