4. The brothers found a treasure of gold and silver. They divided it so that each received 100 kg. The eldest received the most gold - 25 kg - and one eighth of all the silver. How much gold was in the treasure?
Solution. 1) The elder brother received 75 kg of silver, which is one-eighth of the total amount; therefore, the total mass of silver is 600 kg.

2) The others received more silver than the elder brother, i.e., each received more than 75 kg. If there are at least eight brothers, then in total they would receive more than 600 kg; therefore, there are no more than seven brothers.
3) But there must be at least seven of them, since the mass of the silver is 600 kg, which means the total mass of the treasure is more than 600 kg. Therefore, there are seven brothers.
4) The total mass of the treasure is 700 kg, so the mass of the gold is $700-600=100$ kg.

Criteria. The same as in problem 5.6.