Hello, juvenilepunk!

26. If two opposite angles of a quadrilateral measure 120°,

and the measure of the other angles are multiples of 10°,

what is the probability that the quadrilateral is a parallelogram?

The four interior angles of a quadrilateral add up to 360°.

Since , then: .

Since are multiples of 10°, there are 11 cases.

. .

. .

In only one case the quadrilateral is a parallelogram.

Code:

A * - - - - - - - - - * B
/ 120° 60° /
/ /
/ /
/ /
/ 60° 120° /
D * - - - - - - - - - * C

Therefore: .