40 can be said as "forty" in English. This number comes from the English language's base ten number system, which is a system that uses ten different digits (0, 1, 2, 3, 4, 5, 6, 7, 8, and 9) to represent numbers.

Here are some examples of how "forty" can be used in English sentences:

"I have forty dollars in my wallet." (我钱包里有四十美元。)

"The temperature outside is forty degrees Celsius." (外面的温度是四十摄氏度。)

"The bus ride takes forty minutes." (坐公交车要四十分钟。)