A chord of the larger among two concentric circles is of length 10 cm and it is tangent to the smaller circle. What is the area (in cm2) of the annular portion between the two circles?

For two concentric circles, if a chord of the larger circle (length 10 cm) is tangent to the smaller circle, then the perpendicular from the center bisects the chord. This creates a right triangle with half the chord (5 cm) and the radius of the smaller circle as legs. By Pythagoras theorem: R² = 5² + r². The annular area = π(R² - r²) = π(25) = 25π cm².