Final answer:
Bar graphs are ideal for comparing the purchasing amounts of different customer groups by visually representing each group with bars of corresponding lengths. Pie charts are useful as well when there are fewer groups to display the division of total purchases among them.
Step-by-step explanation:
When considering visualizations for showing the purchasing amounts of different groups of customers, bar graphs and pie charts are often the most useful. Bar graphs are excellent for comparing quantities, making it easy to see at a glance which customer group is purchasing more.
For example, each bar can represent a different group of customers with the length or height of the bar corresponding to the purchasing amounts. On the other hand, pie charts can show how the total purchasing volume is divided among different customer groups, especially when there are a smaller number of groups, as too many slices can make a pie chart difficult to interpret.