GUESS A MISSING NUMBER.
I have picked 8 of the numbers from 1 through 9 and hidden them in circles in the diagram below.
Each circle has a line passing through it;
the tally line AB gives sums of the numbers on each line.
Give two methods of finding the number I did not pick.
The next two diagrams show how to do the same trick writing the numbers along the sides of a triangle or a quadrilateral.
の訳を聞きたいんですが...お願いします。