You can put this solution on YOUR website! The two supplementary angles total 180 degrees by definition.
They have a ratio of 11:13, so we can define:
11x + 13x = 180
24x = 180
x = 180/24
x = 15/2
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11x = 11*15/2 = 165/2 = 82.5
13x = 13*15/2 = 195/2 = 97.5
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Do they total 180 degrees?
82.5 + 97.5 = 180.
Yes.
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Is their ratio 11:13?
82.5/97.5 = 11/13.
Correct.
.
The supplementary angles are 82.5 and 97.5 degrees.
.
Done.