The sentence provided is:

"Four is no less than the quotient of a number $x$ and 2.1."

To write this as an inequality:

• "Four is no less than" indicates that the number 4 is greater than or equal to the other expression.
• "The quotient of a number $x$ and 2.1" means $\frac{x}{2.1}$.

Thus, the inequality would be:

$4 \geq \frac{x}{2.1}$

This is the inequality that represents the sentence.

Would you like further details or have any questions about this?

Here are five related questions to expand on this topic:

1. How do you solve the inequality $4 \geq \frac{x}{2.1}$?
2. What happens if you reverse the inequality?
3. How would the inequality change if "no less than" were replaced with "greater than"?
4. Can you graph the solution of $4 \geq \frac{x}{2.1}$?
5. How would this inequality change if the number 2.1 were replaced with another number?

Tip: Inequalities often involve reversing the inequality symbol when you multiply or divide both sides by a negative number.