Penalty for first day = ₹ 200
Penalty for second day = ₹ 250
Penalty for third day = ₹ 300
It is given that penalty for each succeeding day is ₹ 50 more than the preceding day.
This makes it an arithmetic progression because the difference between consecutive terms is constant.
We want to know how much money the contractor has to pay as penalty, if he has delayed the work by 30 days.
So, we have an AP of the form 200, 250, 300, 350....30 terms
First term =a=200
Common difference =d=50
n=30
Applying formula, Sn=n2(2a+(n−1)d) to find sum of n terms of AP , we get
Sn=302(400+(30−1)50)
=15(400+29×50)
=15(400+1450)
=27750
Therefore, penalty for 30 days is ₹ 27,750.