ten speaker can address in 10! ways.......including S1 S2 S3
now s1 s2 s3 can be arranged in 3! ways=6ways i.e s1s2s3 , s1s3s2,s2s1s3,s2s3s1,s3s1s2,s3s2s1
since we want only the order s1 s2 s3 we will take 1/6 th of the total....
so no of ways such that S1speaks before S2 and S2 speaks before S3 is (1/6)10!
no of ways in which ten speaker can address is 10! ways