Final answer:
The cost of the lamp decreased by 45%.
Step-by-step explanation:
To find the percent decrease in the cost of the lamp, we need to calculate the difference between the original cost and the reduced cost, and then divide it by the original cost. The formula for percent decrease is: (Original Cost - Reduced Cost) / Original Cost × 100%. In this case, the original cost is $40 and the reduced cost is $22. So, the percent decrease is: (40 - 22) / 40 × 100% = 18 / 40 × 100% = 45%.
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