Question 14
Sanja has two bowls containing numbered balls. In the left bowl, there are seven balls with the numbers 1, 2, 6, 7, 10, 11 and 12. Their arithmetic mean is 7.0. In the right bowl there are five balls with the numbers 3, 4, 5, 8 and 9; their arithmetic mean is 5.8. Sanja wants to increase the arithmetic mean of the numbers in both bowls. Which ball must she transfer from the left bowl to the right to do this? 