The area of a trapezium is $475 \mathrm{~cm}^{2}$ and its height is $19 \mathrm{~cm}$. Find the lengths of its two parallel sides if one side is $4 \mathrm{~cm}$ greater than the other.
In the given figure, ABCD is a trapezium with parallel sides AB and CD.
Let the length of CD be x.
Then, the length of AB be x + 4.
Area of trapezium $=\frac{1}{2} \times$ sum of parallel sides $\times$ height
$\Rightarrow 475=\frac{1}{2} \times(x+x+4) \times 19$
$\Rightarrow 475 \times 2=19(2 x+4)$
$\Rightarrow 950=38 x+76$
$\Rightarrow 38 x=950-76$
$\Rightarrow 38 x=874$
$\Rightarrow x=\frac{874}{38}$
$\Rightarrow x=23$
∴ The length of CD is 23 cm and the length of AB is 27 cm.
Hence, the lengths of two parallel sides is 23 cm and 27 cm.
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