1. The problem states: The product of 5 and an unknown number is 40. 2. Let the unknown number be $u$. 3. The word "product" means multiplication, so "the product of 5 and $u$" is written as $5 \times u$ or simply $5u$. 4. The phrase "is 40" means equals 40, so we write $= 40$. 5. Combining these, the equation is: $$5u = 40$$ 6. We are asked to write the equation only, not to solve it. Therefore, the equation representing the word statement is: $$5u = 40$$