Final answer:
The common assumption of cost estimation is that it is based on historical data. Cost estimates are derived from past data, such as the cost of similar projects or activities. They may be subject to change over time.
Step-by-step explanation:
The common assumption of cost estimation is that it is based on historical data. Cost estimates are derived from past data, such as the cost of similar projects or activities. By analyzing historical data, we can make informed estimates about future costs.
It is important to note that cost estimates are not always accurate or fixed. They may be subject to change over time due to various factors such as inflation, changes in market conditions, or unexpected events.