How many observations are written to the work.report data set from work.sales?

To understand why the answer is three, it is important to consider how SAS handles data sets and the conditions through which observations are processed. The work.sales data set contains records that may have conditions applied for filtering based on certain criteria, such as a WHERE clause, a conditional statement in a DATA step, or the PROC SORT procedure.

If the original work.sales data set contained observations filtered by specific criteria, the resulting count of observations in work.report would correspond to the number of records that met those criteria. For instance, if the filtering step specified certain product types or sales amounts, these conditions would determine which records appear in the work.report data set.

The calculation of observations might also take into account the presence of data manipulations such as merging or joining with other data sets, which can increase or decrease the final count of records based on joins that yield matching or non-matching records.

Thus, understanding the transformation and criteria leading to the final written observations is pivotal. The data processing context helps establish that three observations satisfy the outlined conditions when populating the work.report data set from work.sales. This aligns with the expected understanding of data management in SAS.