**Answer:**

The fineness modulus (FM) is a measure of the fineness of a sand sample. It is calculated by summing up the cumulative percentages of sand particles retained on each of the standard sieves and dividing it by 100. The resulting value is then divided by 10 to obtain the fineness modulus.

The fineness modulus ranges from 0.1 to 10, and it is commonly used to classify sand into different grades based on its fineness. In this case, the given fineness modulus of 2.7 indicates that the sand is classified as medium sand.

**Explanation:**

To understand why a fineness modulus of 2.7 corresponds to medium sand, let's look at the classification ranges for different types of sand based on their fineness modulus:

- Very fine sand: FM < />
- Fine sand: 1.5 ≤ FM < />
- Medium sand: 2.5 ≤ FM < />
- Coarse sand: FM ≥ 3.5

Since the given fineness modulus of 2.7 falls within the range of 2.5 to 3.5, the sand is categorized as medium sand.

The fineness modulus is an important parameter in determining the gradation and particle size distribution of a sand sample. It provides information about the relative proportions of different-sized particles present in the sand.

A lower fineness modulus indicates a higher proportion of fine particles, while a higher fineness modulus indicates a higher proportion of coarse particles. Therefore, a fineness modulus of 2.7 suggests that the sand sample has a moderate proportion of fine and coarse particles, making it suitable for various construction and engineering applications.

It's worth noting that the classification of sand based on fineness modulus may vary depending on the specific standards or guidelines used in different regions or industries. Therefore, it is essential to consider the context and reference standards when interpreting the classification of sand based on its fineness modulus.