This is the question of arithmetic progression chapter in which we are to calculate the amount of money the contractor has to pay as penalty if he has delayed the work by 30 days if a contract on construction job specifies a penalty for delay of completion beyond a certain date as follows: Rs. 200 for the first day, Rs. 250 for the second day, Rs. 300 for the third day, etc., the penalty for each succeeding day being Rs. 50 more than for the preceding day.
Book RS Aggarwal, Class 10, Chapter 5C, question no 48.
The money the contractor has to pay as a penalty forms an A.P.
We know,
Sn=2n[2a+(n−1)d] ………… (Sum of n terms)
a= First term
d= Common difference
n= number of terms
Here,
a=200,d=50 and n=30
S30=30/2(400+50×29)=27750