1995 AMC 8 Problem 13

Attempt Problem 13 of the 1995 AMC 8 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1995 AMC 8 solutions, or check the answer key.

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13.

In the figure, ∠A,\angle A, ∠B\angle B and ∠C\angle C are right angles. If ∠AEB=40∘\angle AEB = 40^\circ and ∠BED=∠BDE,\angle BED = \angle BDE, then ∠CDE=\angle CDE =

75∘75^\circ

80∘80^\circ

85∘85^\circ

90∘90^\circ

95∘95^\circ

Answer: E
Concepts:angle chasingangle sum
Difficulty rating: 1150
Small Hint:

In triangle BDE,BDE, the angles at EE and DD are equal and ∠B=90∘\angle B = 90^\circ

Big Hint:

∠AED=∠AEB+∠BED;\angle AED = \angle AEB + \angle BED; then use quadrilateral AEDC,AEDC, whose angles sum to 360∘360^\circ

Solution:

In triangle BDE,BDE, the angles at EE and DD are equal and ∠B=90∘,\angle B = 90^\circ, so ∠BED=∠BDE=45∘.\angle BED = \angle BDE = 45^\circ.

Then ∠AED=∠AEB+∠BED\angle AED = \angle AEB + \angle BED =40∘+45∘= 40^\circ + 45^\circ =85∘.= 85^\circ. In quadrilateral AEDC,AEDC, the angles at AA and CC are 90∘,90^\circ, so

∠CDE=360∘−90∘−90∘−85∘=95∘. \begin{aligned} \angle CDE &= 360^\circ - 90^\circ - 90^\circ \\ &\quad {}- 85^\circ \\ &= 95^\circ. \end{aligned}

Thus, the correct answer is E .

Problem 12#12
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