The correct answer is: $1.5748031496\text{ in}$
Explanation
We use the exact conversion factor $1\text{ in}=25.4\text{ mm}$.
Steps:
- Convert millimetres to inches: $$\text{inches}=\frac{40\text{ mm}}{25.4\text{ mm/in}}$$
- Compute the division: $$\text{inches}=\frac{40}{25.4}=1.5748031496\text{ in}$$
- Rounded to a practical number of decimals:
- To three decimals: $1.575\text{ in}$
- To two decimals: $1.57\text{ in}$
Therefore, 40 mm ≈ $1.5748\text{ in}$ (about $1.575\text{ in}$).
Note: If you mean nominal pipe size (common plumbing/pipe terms), the nominal inch sizes do not always equal the actual outside diameter; tell me the context if you need the nearest standard pipe size instead.