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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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EDUCART PUBLICATION-ARITHMETIC PROGRESSIONS-LONG ANSWER TYPE QUESTIONS
  1. In an AP, if a = 1, a(n)= 20 and S(n) = 399, then n is equal to

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  2. The 26th, 11th and the last terms of an AP are, 0, 3 and -(1)/(5),resp...

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  3. Find the sum of the following series : 5+(-41)+9+(-39)+13+(-37)+17+....

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  4. The sum of four consecutive numbers in A.P. is 32 and the ratio of the...

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  5. Solve for x: 1+4+7+10+...+x=287

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  6. The sum of the first five terms of an A.P. and the sum of the first s...

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  7. Find the (i) sum of those integers between 1 and 500 which are multi...

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  8. Find the (i) sum of those integers between 1 and 500 which are multi...

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  9. Find the (i) sum of those integers between 1 and 500 which are multi...

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  10. An AP consists of 37 terms. The sum of the three middle most terms is ...

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  11. If the sum of first p terms of an A.P. is equal to the sum of the firs...

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  12. Find the sum of the integers between 100 and 200 that are divisible by...

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  13. Find the sum of the integers between 100 and 200 that are divisible by...

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  14. Which term of the Arithmetic Progression -7, - 12, -17, -22,… will be ...

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  15. How many terms of the arithmetic progression 45, 39, 33,….. Must be ta...

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  16. Show that the sum of an AP whose first term is a, the second term b an...

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  17. If the sum of the first four terms of an AP is 40 and the sum of the f...

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  18. The sum of the 4th and 8th terms of an AP is 24 and the sum of the ...

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  19. If the ratio of the 11^(th) term of an AP to its 18^(th) term is 2 : 3...

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  20. The ratio of the sums of m terms and n terms of an A.P. is m^(2) : n^(...

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  21. Solve the equation -4+(-1)+2+ … +x =437.

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