SOLUTION: The twenty first term of an ap is five and a half while the sum of the twenty one terms is ninetyfour and a half.find the sum of the first 3 terms of the ap
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Question 1141684: The twenty first term of an ap is five and a half while the sum of the twenty one terms is ninetyfour and a half.find the sum of the first 3 terms of the ap Answer by greenestamps(13203) (Show Source):
(1) The sum of 21 terms of an AP is 21 times the average of the first and last. Let the first term be x; then
Solve to find the first term.
(2) The 21st term is the first term plus the common difference d 20 times. Use the given 21st term and the first term from (1) above to find the common difference d.
(3) Use the common difference and the first term to find the second and third terms.
(4) Add the first three terms to get the answer to the problem.
