Answer:
The correct answers will be- when the scientists do not not get the expected results in the form of the exact numbers.
Explanation:
Estimation is the process of approximation based on the uncertain or unexpected, unstable and incomplete data.
The process of estimation is sometimes followed by the scientists like when predicting the exact age of the Earth or the evolutionary facts of species which is impossible to predict and the data does not provide the exact numbers.
Thus, scientist relies on estimated when they do not get the expected results in the form of exact numbers.