A district manager rewards sales teams based on overall sales generated in a month. The data for earnings are shown in the table, where Low represents the lowest sales and High represents the highest sales generated by a single sales team member. σ
Team X190228020901005.9921.5841.75542.7< br /> Team Y745182010751165.51147.5447262.1
Team Z950227513251906.62015.5362.3283.6< br />
Part A: If the manager wants to award the sales team that has the most consistent earnings among its team members, which team should it choose and why? Justify your answer mathematically.

Part B: If the manager wants to award the sales team with the highest average earnings, which team should it choose and why? Justify your answer mathematically.