How to find the perimeter of a parallelogram

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PSAT Math › How to find the perimeter of a parallelogram

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ABCD is a parallelogram. BD = 5. The angles of triangle ABD are all equal. What is the perimeter of the parallelogram?

Figure_1

$15\sqrt{3}$

$10\sqrt{3}$

$11\sqrt{2}$

If all of the angles in triangle ABD are equal and line BD divides the parallelogram, then all angles in triangle BDC must be equal as well.

We now have two equilateral triangles, so all sides of the triangles will be equal.

All sides therefore equal 5.

5+5+5+5 = 20