The 8 1 box is divided into three parts, and each part has 27 boxes. It is easy to understand that 1 time can confirm that these 27 boxes are inside.
Twenty-seven boxes were divided into three parts, 9 boxes in each part, and weighed 1 time to determine which 9 boxes were the same.
Divide 9 boxes into 3 parts and weigh 1 time to determine which 3 boxes are the same.
Divide three boxes into three parts, each part is 1 box, and then call it 1 time. Determine which one is 1 box in the same way.
It takes four times to find this box of chalk.