One of the congruent angles of the isosceles triangle given above is 40° which means that the other angle, mPRQ is also 40°. Knowing that the sum of the angles of a triangle is 180°, mPQR may be calculated by,
mPQR = 180 - (mPRQ + mQPR)
Subsituting the given,
mPQR = 180 - (40 + 40) = 100°
Thus, the answer is 100°.
