Three concentric circles have diameters in arithmetic progression. Smallest circumference is 8π cm, largest is 18π cm. What is the middle circumference?

సమాధానం చూపించు & వివరణ

సమాధానం: (C) 13π cm

వివరణ

Diameters 8 and 18, so the middle is 13: circumference 13π.