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Sticky Note
An arithmetic progression has 2nd term = 20 and 8th term = 60. What is the 20th term?
  1. 100
  2. 140
  3. 180
  4. 200
Explanation

aₙ = a + (n - 1)d


Let a be the first term, d the common difference.


Given:  

2nd term: a + d = 20  

8th term: a + 7d = 60


Subtract the two equations:  

(a + 7d) - (a + d) = 60 - 20  

6d = 40 ⇒ d = 40 / 6 = 20 / 3


Now plug d = 20/3 into a + d = 20:  

a = 20 - 20/3 = (60 - 20)/3 = 40/3


Now find the 20th term:  

a + 19d = 40/3 + 19 × (20/3) = (40 + 380)/3 = 420/3 = 140

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  1. 31.4
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