The  sum of first 24 terms of the A.P, a1,a2,a3,.... if it is known that  a1+a5+a10+a15+a20+a24=225

We known that in an A.P the sum of the termsequidistant  from the beginning and end is always same and is equal tothe sum of first and last term, ie. a1+an=a2+an−1=a3+an−2=.....So if an A.P. consists  of 24 terms, then a1+a24=a3+a20=a10+a15a1+a5+a10+a15+a20+a24=225⇒a1+a24=2253=75∴S24=242a1+a24usin⁡gSn=n2a1+an=12(75)=900( using (i))