2023 AMC 10B Problem 7

Below is the professionally curated solution for Problem 7 of the 2023 AMC 10B, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2023 AMC 10B solutions, or check the answer key.

All of the real AMC 8, AMC 10, AMC 12, and AIME problems in our complete solution collection are used with official legal permission of the Mathematical Association of America (MAA).

Concepts:angle chasingisosceles triangletransformation

Difficulty rating: 1310

7.

Square ABCDABCD is rotated 2020^\circ clockwise about its center to obtain square EFGH,EFGH, as shown below. What is the degree measure of EAB?\angle EAB?

2424^\circ

3535^\circ

3030^\circ

3232^\circ

2020^\circ

Solution:

Let OO be the shared center. The rotation carries AA to E,E, so OA=OEOA = OE and AOE=20.\angle AOE = 20^\circ. That makes triangle OAEOAE isosceles, with base angles OAE=180202=80.\angle OAE = \frac{180^\circ - 20^\circ}{2} = 80^\circ. The diagonal ACAC splits the right angle at A,A, so OAB=45.\angle OAB = 45^\circ. Subtracting, EAB=8045=35.\angle EAB = 80^\circ - 45^\circ = 35^\circ. Thus, B is the correct answer.

Problem 7 in Other Years