1988 AMC 8 Problem 5 — Solution | LIVE by Po-Shen Loh

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1988 AMC 8 Problem 5

Below is the professionally curated solution for Problem 5 of the 1988 AMC 8, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1988 AMC 8 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 chasing

Difficulty rating: 800

5.

If $\angle CBD$ is a right angle, then this protractor indicates that the measure of $\angle ABC$ is approximately

$20^\circ$

$40^\circ$

$50^\circ$

$70^\circ$

$120^\circ$

Solution:

Reading the protractor, ray $BA$ is at about $20^\circ$ and ray $BD$ is at about $160^\circ.$

Because $\angle CBD$ is a right angle, ray $BC$ is at $160^\circ - 90^\circ = 70^\circ.$

Therefore $\angle ABC = 70^\circ - 20^\circ = 50^\circ.$

Thus, the correct answer is C .

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