Join OA and OC. Let the radius of the circle be r cm and O be the centre Draw OP⊥AB and OQ⊥CD. We know, OQ⊥CD, OP⊥AB and AB∥CD. Therefore, points P,O and Q are collinear. So, PQ=6 cm. Let OP=x. Then, OQ=(6–x) cm. And OA=OC=r. Also, AP=PB=2.5 cm and CQ=QD=5.5 cm. (Perpendicular from the centre to a chord of the circle bisects the chord.) In right triangles QAP and OCQ, we have OA2=OP2+AP2 and OC2=OQ2+CQ2 ∴r2=x2+(2.5)2 ..... (1) and r2=(6−x)2+(5.5)2 ..... (2) ⇒x2+(2.5)2=(6−x)2+(5.5)2 ⇒x2+6.25=36−12x+x2+30.25 12x=60 ∴x=5 Putting x=5 in (1), we get r2=52+(2.5)2=25+6.25=31.25 ⇒r2=31.25⇒r=5.6 Hence, the radius of the circle is 5.6 cm