Solution Step 0/0
Suppose, you have two lengths of rope, and you know that each of them will take exactly one hour to burn. However, the rope varies in thickness and some parts may burn at different speeds, so half of a 1-hour length may take more or less than half an hour to burn.
They say it is possible to use the ropes to measure exactly 45 minutes, with no timepieces and without doing any cuts to the ropes.
How many flames would you need to complete the task?
They say it is possible to use the ropes to measure exactly 45 minutes, with no timepieces and without doing any cuts to the ropes.
How many flames would you need to complete the task?
Explanations
4 flames in total.Step 1. Light both ends of the first rope and one end of the second rope (three separate flames).
Step 2. When the first rope has burned all the way, 30 minutes have elapsed. Light the other end of the second rope (the fourth flame).
Step 3. When the remainder of the second rope (1/2 of its initial length) has burned all the way, another 15 minutes have elapsed.
Even though parts of the rope may be burning at different rates, when you light both ends, you are still cutting the time in half.
Check 2 flames
Check 3 flames
Check 4 flames
Check 5 flames
