ISEE Upper Level Math : How to find an angle in other quadrilaterals

Study concepts, example questions & explanations for ISEE Upper Level Math

varsity tutors app store varsity tutors android store

Example Questions

Example Question #1 : Quadrilaterals

Three of the interior angles of a quadrilateral measure \(\displaystyle 51^{\circ }\)\(\displaystyle 120 ^{\circ }\), and \(\displaystyle 77^{\circ}\). What is the measure of the fourth interior angle?

Possible Answers:

\(\displaystyle 102^{\circ }\)

\(\displaystyle 112^{\circ }\)

\(\displaystyle 122^{\circ }\)

This quadrilateral cannot exist.

\(\displaystyle 92^{\circ }\)

Correct answer:

\(\displaystyle 112^{\circ }\)

Explanation:

The measures of the angles of a quadrilateral have sum \(\displaystyle 360^{\circ }\). If \(\displaystyle x\) is the measure of the unknown angle, then:

\(\displaystyle x + 51 + 120 + 77 = 360\)

\(\displaystyle x + 248 = 360\)

\(\displaystyle x + 248 -248 = 360-248\)

\(\displaystyle x = 112\)

The angle measures \(\displaystyle 112^{\circ }\).

Example Question #1 : How To Find An Angle In Other Quadrilaterals

The angles of a quadrilateral measure \(\displaystyle x^{\circ }, x^{\circ }, \left ( x+45 \right ) ^{\circ }, \left ( x+65 \right ) ^{\circ }\). Evaluate \(\displaystyle x\).

Possible Answers:

\(\displaystyle x = 70\)

\(\displaystyle x = 62.5\)

\(\displaystyle x = 67.5\)

\(\displaystyle x = 65\)

Correct answer:

\(\displaystyle x = 62.5\)

Explanation:

The sum of the degree measures of the angles of a quadrilateral is 360, so we can set up and solve for \(\displaystyle x\) in the equation:

\(\displaystyle x + x + \left ( x+45 \right ) + \left ( x+65 \right ) = 360\)

\(\displaystyle 4x+110= 360\)

\(\displaystyle 4x+110- 110 = 360 - 110\)

\(\displaystyle 4x = 250\)

\(\displaystyle 4x\div 4 = 250 \div 4\)

\(\displaystyle x = 62.5\)

Example Question #1 : Quadrilaterals

The four angles of a quadrilateral have the following value: 79 degrees, 100 degrees, 50 degrees, and \(\displaystyle 2x\) degrees. What is the value of \(\displaystyle x\)?

Possible Answers:

\(\displaystyle 65.5\)

\(\displaystyle 131\)

\(\displaystyle 130\)

\(\displaystyle 65\)

Correct answer:

\(\displaystyle 65.5\)

Explanation:

Given that there are 360 degrees when all the angles of a quadrilateral are added toghether, this problem can be solved with the following equation:

\(\displaystyle 360 = 79 +100 +50 + 2x\)

\(\displaystyle 360=229+2x\)

\(\displaystyle 131=2x\)

\(\displaystyle x=65.5\)

Example Question #231 : Plane Geometry

In a quadrilateral, the angles have the following values:

\(\displaystyle 94^{\circ},27^{\circ},81^{\circ},\textup{and }(4x)^{\circ}\)

What is the value of \(\displaystyle x\)?

Possible Answers:

\(\displaystyle 40\)

\(\displaystyle 51\)

\(\displaystyle 39.5\)

\(\displaystyle 158\)

Correct answer:

\(\displaystyle 39.5\)

Explanation:

Given that there are 360 degrees when the angles of a quadrilateral are added together, it follows that:

\(\displaystyle 94 + 27+ 81 + 4x =360\)

\(\displaystyle 202+4x=360\)

\(\displaystyle 4x=158\)

\(\displaystyle x=39.5\)

Learning Tools by Varsity Tutors