If x is a real number and x < 5, which point is the boundary point on the number line?

Correct answer: 5

The governing concept is the boundary, or critical, point of a linear inequality. In x < 5, the variable is compared directly with the constant 5, so the solution region changes at x = 5. Values such as 4 and 0 lie to the left and satisfy the inequality, whereas values such as 6 lie to the right and do not. Because the sign is strictly less than, the point 5 itself is not included and would be shown by an open circle; however, it remains the boundary point. Thus option C, 5, is correct. The numbers 0, 1, and −5 are possible solution values, not the point where the direction changes.