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Re: In the figure above, if DE is parallel to ВС, what is t [#permalink]
14 Feb 2011, 16:08

Expert's post

Attachment:

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In the figure above, if DE is parallel to ВС, what is the sum of the degree of angle ADE and angle ACB?

As DE is parallel to ВС then <D=<B and <E=<C. Question: <D+<C=?

(1) AB = BC --> <A=<C --> <A+<C+<B=180 (sum of the interior angles of a triangle is 180 degrees) --> 2*<C+<B=180 --> as <D=<B then 2*<C+<D=180 --> <D+<C=180-<C. Not sufficient.

(2) Angle A is 70 degree. <A+<C+<B=180 --> 70+<C+<D=180 --> <D+<C=110. Sufficient.

Re: In the figure above, if DE is parallel to ВС, what is t [#permalink]
14 Feb 2011, 17:37

Hi Bunuel, I am sure I may be missing something, but why not answer is B, we need to find <D + <C or <D+<E since <C = <E, since <A is 70, <D+<E = 110 or <D+<C = 110 ?

Re: In the figure above, if DE is parallel to ВС, what is t [#permalink]
14 Feb 2011, 17:53

Expert's post

brandy96 wrote:

Hi Bunuel, I am sure I may be missing something, but why not answer is B, we need to find <D + <C or <D+<E since <C = <E, since <A is 70, <D+<E = 110 or <D+<C = 110 ?

You are not missing anything: for some reason I was calculating <D+<A for (2) not <D+<C. Edited. _________________