Angles are named by their size: an acute angle is smaller than a right angle, a right angle measures exactly 90 degrees, an obtuse angle is bigger than a right angle but smaller than a straight line, and a straight angle is 180 degrees. On this fifth grade sheet a child sees twelve angles drawn with their measure written on them and writes the name of each one.
Because every angle has its measure printed, the work is knowing what the numbers mean, not guessing from the picture. Each version has different angles, and the answer key gives every name.
What your child will learn
Know the size of a right angle
Name acute and obtuse angles
Recognize a straight angle
Use the measure to classify
Common Core standard: 4.MD.C.5
Worked example
A 35-degree angle is smaller than 90 degrees, so it is acute. A 120-degree angle is obtuse.
Common mistake
Calling a 90-degree angle acute or obtuse; exactly 90 degrees is a right angle.
Helpful hint
Compare the measure with 90 and 180: less than 90 is acute, exactly 90 is right, between 90 and 180 is obtuse, 180 is straight.