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For an A.P the sum of first 30 terms is -1155,the common difference is -3and the thirtieth term is -82. What is the first term?
  • a)
    10 
  • b)
    8
  • c)
    5
  • d)
    12
Correct answer is option 'C'. Can you explain this answer?
Verified Answer
For an A.P the sum of first 30 terms is -1155,the common difference is...
l = a + (n - 1)d
Where l = -82,a = ?,d = -3,n = 30
-82 = a + 29 (- 3)
a = 5
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Most Upvoted Answer
For an A.P the sum of first 30 terms is -1155,the common difference is...
Given: sum of first 30 terms = -1155, common difference = -3, thirtieth term = -82

To find: first term

Formula to find the sum of first n terms of an AP:

S_n = n/2[2a + (n-1)d]

where S_n is the sum of first n terms, a is the first term, d is the common difference.

Using the given values, we can form the equation:

-1155 = 30/2[2a + (30-1)(-3)]

-1155 = 15[2a - 87]

-1155 = 30a - 1305

30a = 150

a = 5

Therefore, the first term of the AP is 5. Hence, option (c) is the correct answer.
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For an A.P the sum of first 30 terms is -1155,the common difference is...
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For an A.P the sum of first 30 terms is -1155,the common difference is -3and the thirtieth term is -82. What is the first term?a)10b)8c)5d)12Correct answer is option 'C'. Can you explain this answer?
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