An important and exam oriented question from arithmetic progression chapter as it was already asked in previous year paper of 2015 in which we are to calculate the last term and its sum of last 15 terms, if An AP 5, 12, 19,……has 50 terms.
Book RS Aggarwal, Class 10, chapter 5C, question no 34(i)
a=5,d=12−5=7,n=50
Last term,
an=a+(n−1)d
=5+(50−1)7=348
Sn=n/2[2a+(n−1)d]
=50/2[2(5)+(50−1)7]
=25[10+49×7]
=8825