The circumference of two concentric rings is 88 cm and 66 cm respectively. Then the width between the rings is

Circumference of other ring $2\pi R_1=88$ cm

Circumference of inner ring $2\pi R_1=66$ cm

$\therefore 2\pi R_1=88$

$2\times \frac{22}{7}\times R_1=88$

$R_1=88\times \frac{7}{44}$

$R_1=$ 14 cm

$2\pi r_1=66$

$2\times \frac{22}{7}\times r_1=66$

$r_1=66\times \frac{7}{44}$

$r_1=\frac{21}{2}=$ 10.5 cm

Width of a rings $=$ $14-10.5$ cm$=$ 3.5cm