Level 3
In a room with a certain number of people, each person shook hands with the rest of the people only once. The total number of handshakes is 78. How many people are there in the room?
Level 3
The figure shows the first 3 triangular patterns which are formed with circles. How many circles are needed to form the 7th triangular pattern?
Level 3
The figure shows the first 3 triangular patterns which are formed with circles. How many circles are needed to form the 7th triangular pattern?