Final answer:
The decay factor for an Apple MAC depreciating at 20% yearly is 0.80, representing 80% of the device's value that remains after each year.
Step-by-step explanation:
The depreciation of an Apple MAC that costs $1500 at a rate of 20% yearly involves finding the decay factor. The decay factor represents the percentage of the item's value that remains after each year. In this case, if the device depreciates by 20% each year, 100% - 20% = 80% of its value remains.
To express this as a decay factor (base), you use the remaining percentage in decimal form. Therefore, the decay factor is 0.80. This means that each year, the device will be worth 80% of its value from the previous year.