SOLUTION: the 6th term is 50 and the 11th term is 85 find the 21st term

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Question 1074275: the 6th term is 50 and the 11th term is 85 find the 21st term
Answer by ikleyn(52788) About Me  (Show Source):
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The 6th term highlight%28of_an_AP%29 is 50 and the 11th term is 85. Find the 21st term highlight%28of_the_progression%29.
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a%5B6%5D  = a%5B1%5D+%2B+5%2Ad  = 50,   (1)
a%5B11%5D = a%5B1%5D+%2B+10%2Ad = 85.   (2)

=====>  5d = 85 - 50 = 35.   ====>  d = 7.


a%5B21%5D = a%5B11%5D%2B10%2Ad = 85 + 10*7 = 155.

Solved.


There is a bunch of lessons on arithmetic progressions in this site:
    - Arithmetic progressions
    - The proofs of the formulas for arithmetic progressions
    - Problems on arithmetic progressions
    - Word problems on arithmetic progressions
    - Mathematical induction and arithmetic progressions
    - One characteristic property of arithmetic progressions
    - Solved problems on arithmetic progressions


Also,  you have this free of charge online textbook in ALGEBRA-II in this site
    - ALGEBRA-II - YOUR ONLINE TEXTBOOK.

The referred lessons are the part of this online textbook under the topic "Arithmetic progressions".