Let us define as a part of the angle XDE is the angle BDE formed when dividing the angle XDE by the ray DB, knowing by the problem statement that the angle XDB is 0.4 of the angle XDE:
1 – 0.4 = 0.6.
Let us determine the degree measure of the angle BDE, knowing by the statement of the problem that the angle XDE is right and which means, in turn, that its degree measure is 90 °:
90 * 0.6 = 54.
Answer: The degree measure of the angle BDE, which is formed when the angle XDE is divided by the ray DB, is 54 °.
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