Chapter 1 - Foundations for Algebra - 1-3 Real Numbers and the Number Line - Practice and Problem-Solving Exercises - Page 20: 23

18

The problem asks us to estimate the square root to the nearest integer answer, so we consider the closest square root that gives us an integer answer. We know that the square root of 324 is 18. The square root of 324 is fairly close to the square root of 320, so 18 is a good approximation for the square root of 320.