Please tell

Asked by  | 17th Dec, 2008, 05:51: AM

Expert Answer:

treat it as n A.P.  with first term as 51 and common difference as -1.Then 21 will be the 31st term. So  use the formula

 Sum of an A.P.  with first term as a and last term as l, where there are n terms is given by

S=n/2{a+l}

Answered by  | 17th Dec, 2008, 07:55: AM

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