Question 1161339
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Tutor @ikleyn shows one efficient way to find the sum, knowing that it is an arithmetic sequence:<br>
(1) use the first term and common difference to find the last (7th) term
(2) find the average of the first and last terms, which is the average of all the terms
(3) multiply that average by the number of terms.<br>
Here is another efficient way....<br>
(1) use the first term and the common difference to find the middle (4th) term, which is the average of all the terms
(2) multiply that average by the number of terms.<br>
middle (4th) term: 10+3(4) = 10+12 = 22
sum: 7(22) = 154<br>