Finding Unknown Angle Measures

4.MD.5.a

“An angle is measured with reference to a circle with its center at the common endpoint of the rays, by considering the fraction of the circular arc between the points where the two rays intersect the circle. An angle that turns through 1/360 of a circle is called a "one-degree angle," and can be used to measure angles.”

The boxed reference facts define the right angle and straight angle in degrees, the totals every problem depends on.

4.MD.5.b

“An angle that turns through n one-degree angles is said to have an angle measure of n degrees.”

Each printed label (35°, 115°, 80° and the rest) is an n-degree measure in this standard's sense.

4.MD.6

“Measure angles in whole-number degrees using a protractor. Sketch angles of specified measure.”

The sheet gives every measure in whole degrees rather than asking students to measure; the labeled diagrams stand in for protractor readings.

4.MD.7

“Recognize angle measure as additive. When an angle is decomposed into non-overlapping parts, the angle measure of the whole is the sum of the angle measures of the parts. Solve addition and subtraction problems to find unknown angles on a diagram in real world and mathematical problems, e.g., by using an equation with a symbol for the unknown angle measure.”

All ten problems. The three-part splits in questions 7 and 8 and the gate-and-fan pair are the standard's real-world equations with a symbol for the unknown.