If A=1.4 and B=2.1 on the number line, what is the length of AB?

Correct answer: 0.7

On a number line, the length between two points is the distance separating their coordinates. Distance cannot be negative, so we use the absolute value of the difference. If one point is at 1.4 and the other is at 2.1, the second point lies to the right of the first. The segment length is therefore found by subtracting the smaller coordinate from the larger one.

Using the distance rule, write AB = \(|2.1 - 1.4|\). The subtraction gives 0.7, and its absolute value is also 0.7. Thus the points are seven-tenths of one unit apart, so option B is correct. The value 1.7 would come from adding the coordinates, which does not measure the distance between points on a number line.