MathDB

5

Part of 1988 AMC 8

Problems(1)

1988 AJHSME #5

Source:

6/21/2011
If ∠CBD \angle\text{CBD} is a right angle, then this protractor indicates that the measure of ∠ABC \angle\text{ABC} is approximately
[asy] unitsize(36); pair A,B,C,D; A=3*dir(160); B=origin; C=3*dir(110); D=3*dir(20); draw((1.5,0)..(0,1.5)..(-1.5,0)); draw((2.5,0)..(0,2.5)..(-2.5,0)--cycle); draw(A--B); draw(C--B); draw(D--B); label("O",(-2.5,0),W); label("A",A,W); label("B",B,S); label("C",C,W); label("D",D,E); label("0",(-1.8,0),W); label("20",(-1.7,.5),NW); label("160",(1.6,.5),NE); label("180",(1.7,0),E);[/asy] (A) 20∘(B) 40∘(C) 50∘(D) 70∘(E) 120∘ \text{(A)}\ 20^\circ\qquad\text{(B)}\ 40^\circ\qquad\text{(C)}\ 50^\circ\qquad\text{(D)}\ 70^\circ\qquad\text{(E)}\ 120^\circ