The penalties form an arithmetic progression (A.P.) with a first term of 200 and a common difference of 50.
\(a = 200\) and \(d = 50\)
The penalty for delaying the work by 30 days is calculated as:
= \(S_{30}\)
= \(\frac {30}{2} [2\times 200 + (30-1)50]\)
= \(15 [400 + 1450]\)
= \(15 (185\)0)
= \(27750\)
Consequently, the contractor must pay a penalty of Rs. 27750.