In an isosceles triangle RST what is the measure of angle R?

Question

Can someone explain the triangle property in the following question:

1) angle t=100 degrees

2) angle s= 40 degrees

govinam · Answer

OA is A....

I don't know why its not D.

asaf · Answer

Can I change it to C?

100 + 40 + 40 = 180

asaf · Answer

Yeah my bad.

we already have 100 so left with only 80. So two other angles had to be 40.

rookie06 · Answer

Its A.

If t=100, then another angle in this triangle cannot be 100 as the sum of all angles in a triangle is 180. So the other two angles must be equal and each has measure of 40 (80/2).

govinam · Answer

If s=40 and it is isosceles, aren't the other two angles automatically the same? Am I confusing rules?

rookie06 · Answer

If s=40, then there are other possibilities.

For example, r & s are isosceles and r=s=40 and t=100.

OR

r & t are isosceles, so r=t=70

So you see r can have different values from statement 2.

yezz · Answer

In an isosceles triangle RST what is the measure of angle R? 

1) angle t=100 degrees 

2) angle s= 40 degrees

IT IS A

ALL INTERIOR ANGLES OF A TRIANGLE = 180
TRIANGLE IS ISOCELES THUS TWO ANGLES HAS THE SAME MEASURE

FROM A ONE ANGLE IS 100

THUS SURE THE OTHER TWO SUM UP TO 80 AND THEY ARE THE EQUIVEKANT ONES 

WE CANT HAVE 2 100 ANGLES

FROM TWO

ONE ANGLE IS 40 THUS WE CAN HAVE TWO OPTIONS OTHER TWO ANGLES ARE = 60 

OR ONE ANGLE = 40 AND THE OTHER IS 100

AND WE KNOW THAT IN GMAT STATMENT ONE AND TWO CANNOT CONTRADICT EACH OTHER.

In an isosceles triangle RST what is the measure of angle R?

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