Find the sum 41118144 Find the sum 41118144Solutiongiven sum

Solution

given sum:4+11+18 + - - -144

       This like an arithmetic progression.

so number of terms of an arithmetic progression

     n=(l-a)/d +1

        here l=144, a=4   d=t2-t1=11-5=7

     n=(144-4/7)+1

     n=(140/7)+1

     n=20+1 =21;

Sum of first n terms in an arithmetic progression:

     S_n=n/2[2a+(n-1)d] =n/2(a+l)

          Here n=21; a=4 ;l=144

         = 21/2(4+144)

        =21/2(148)

        =21(74)

        =1554