Question

Area of a trapezoid is $81{\text{cm}}^2$. Height of the trapezoid is 9 cm. Find the length of the parallel side, if one of the parallel side measures $11$ cm.

• A. 4.5 cm
• B. 18 cm
• C. 7 cm
• D. 9 cm

Answer 1

The correct option is C 7 cm

Lets draw a trapezoid ABCD of the given dimensions.Given,
$BC=11\text{cm}$
Height of the trapezoid $=9\text{cm}$
AD is parallel to BC

Let $AD=x\text{cm}$

As we know,
Area of a trapezoid $=\frac{1}{2}\times$ (sum of the parallel sides)$\times h$

$81=\frac{1}{2}\times (BC+AD)\times DE$

$81=\frac{1}{2}\times (11+x)\times 9$

$18=11+x$

$x=7$ cm

Option (c) is correct.