Subject :IMO Class : Class 8
The points P, Q, R and S lie on a straight line. The ratio of the length of PQ to the length of QR is 3 : 4 and the ratio of the length of PR to the length of RS is 2 : 1. Find the ratio of the length of QR to the length of PS.
A 7 : 19
B 10 : 21
C 21 : 8
D 8 : 21