Final answer:
Jack spent 20% less this month compared to last month.
Step-by-step explanation:
To find the percentage decrease in Jack's spending, we need to calculate the difference in the amounts and find what percentage of the original amount it represents. The difference between $80.00 and $64.00 is $16.00. To find the percentage decrease, we divide the difference by the original amount ($16.00 ÷ $80.00) and then multiply by 100.
Percentage decrease = ($16.00 ÷ $80.00) × 100 = 0.2 × 100 = 20%
This means that Jack spent 20% less this month compared to last month.