A thief is running after stealing two gold bars from an ancient and sacred temple. The villagers see him running and runs after him. While running, he comes across a rope bridge. There is a warning board on the start of the bridge stating that the rope can only accommodate a weight of 130 pounds.
Now the thief weighs 100 pounds and the gold bars weigh 20 pounds each. But ignoring the warning he just crosses the bridge with both gold bars. He manages to cross safely. How?
Solution:
You must be aware of the fact that the standard weighing system is Imperial system. This is how we weigh things or ourselves and thus the warning must be for 130 pounds according to the Imperial system.
But gold is weighed in the Troy system. In Troy system, 12 ounces makes one pound whereas in Imperial system, 16 ounces make one pound.
Thus 40 pounds (20+20) of gold bars will be 30 pounds in imperial system. The weight of thief is 100 pounds. Thus, the total is 130 pounds which can be accommodated on the rope and thus he was able to cross safely.