Question

ABDC is a trapezoid. Line AB = 2.5, and Line EF = 4.5. What is the length of Line CD ?

Answer 1

The line CD is the median of thre trapezoid, therefore its measures is shown below:
 You must sum the largest base and the shortest base and divide both of them by 2, as following:
 CD=(4.5+2.5)/2
 CD=7/2
 CD=3.5
 Therefore, as you can see, the measure of the line CD is 3.5
 The answer is: 3.5

Answer 2

The correct answer is 3.5

A trapezoid is a 4-sided flat shape with straight sides. This shape has a pair of opposite sides parallel. So according to the figure we know the following:

$\overline{AC}=\overline{CE}$

And it is also true that:

$\overline{BD}=\overline{EF}$

We know that the lengths of the parallel sides are given by:

$\overline{AB}=2.5 \\ \\ \overline{EF}=4.5$

So the goal is to find the length of Line CD. This line is in fact the median of the trapezoid (also called a midline or midsegment) that is a line segment half-way between the two bases and it can be found as follows:

$m=\frac{\overline{AB}+\overline{EF}}{2}=\frac{2.5+4.5}{2}=\frac{7}{2} \\ \\ \therefore \boxed{\overline{CD}=m=3.5}$