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In an AP, if a = 1, a(n)= 20 and S(n) = ...

In an AP, if a = 1, `a_(n)`= 20 and `S_(n)` = 399, then n is equal to

A

19

B

21

C

38

D

42

Text Solution

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The correct Answer is:
C
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OSWAL PUBLICATION-ARITHMETIC PROGRESSIONS -NCERT EXAMPLAR (EXERCISE-5.1)
  1. A small terrace at a football ground comprises of 15 steps each of wh...

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  2. In an AP, if d = -4, n = 7 and a(n) = 4, then a is equal to

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  3. In an AP, if a = 3.5, d = 0 and n = 101, then a(n) will be

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  4. The list of number -10, -6, -2, 2, … is

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  5. The 11 ^(th) term of the A.P.:-5,- (5)/(2), 0, (5)/(2),... is

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  6. The first four terms of an A.P. whose first term is -2 and the common ...

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  7. The 21st term of an AP whose first two terms are -3 and 4, is

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  8. If the 2^(nd) term of an A.P. is 13 and the 5^(th) term is 25, what is...

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  9. Which term of the AP 21, 42, 63, 84,.. Is 210?

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  10. If the common difference of an AP is 5, then what is a(18)-a(13) ?

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  11. What is the common difference of an AP in which a(18)-a(14) = 32?

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  12. Two APs have the same common difference. The first term of one of the...

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  13. If 7 times the 7th term of an AP is equal to 11 times its 11th term, t...

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  14. The 4th term from the end of an AP -11, -8, -5, …, 49 is

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  15. The famous mathematician associated with finding the sum of the first ...

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  16. If the first term of an AP is -5 and the common difference is 2, then ...

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  17. The sum of first 16 terms of the A.P.: 10,6,2,... Is

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  18. In an AP, if a = 1, a(n)= 20 and S(n) = 399, then n is equal to

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  19. The sum of first five multiples of 3 is

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