Level 3
The mass of 4 children, Mandy, Nellie, Peter and Richie were taken. Only 3 children can be weighed at one time. Mandy, Nellie and Peter weighed a total of 55 kg. Nellie, Peter and Richie weighed a total of 56 kg. Mandy, Peter and Richie weighed a total of 57 kg. Mandy, Nellie, and Richie weighed a total of 60 kg. What is the average mass of the 4 children?
3 m