Answer: The measure of the fourth angle of the given quadrilateral is 50°.
Step-by-step explanation: Given that a quadrilateral has three angles that measure 90° , 100° and 120°.
We are to find the measure of the fourth angle of the quadrilateral.
Let x° be the measure of the fourth angle of the quadrilateral.
We know that
The sum of the measures of the four angles of a quadrilateral is 360°.
So, for the given quadrilateral, we have
[tex]90^\circ+100^\circ+120^\circ+x^\circ=360^\circ\\\\\Rightarrow 310^\circ+x^\circ=360^\circ\\\\\Rightarrow x^\circ=360^\circ-310^\circ\\\\\Rightarrow x^\circ=50^\circ.[/tex]
Thus, the measure of the fourth angle of the given quadrilateral is 50°.
