An important question from arithmetic progression chapter as it was already asked in previous year paper of 2013 in which we have been asked to prove that 72nd term is 4 times its 15th term, if the 24th term of an AP is twice its 10th term.
Book – RS Aggarwal, class 10, chapter 5A, question no 38
Let a= first term of A.P.,
d= common difference
nth term, a24=2a10
⇒a+23d=2(a+9d)
⇒a+23d=2a+18d
⇒a=5d
Now,
a72/a15=(a+71d)/(a+14d)
=76d/19d
=4.