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Sum of first 55 terms in an A.P, is 3300, find its 28i term. |
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Answer» S55 = 3300 [Given that]Now Sn = n/2[2a + (n – 1)d] ∴S55 = 55/2[2a + (55 – 1) d] ∴3300 = 55/2[2a + 54d] ∴3300 = 55/2 × 2[a + 27d] ∴3300 = 55 [a + 27d] ∴3300/55= a + 27d ∴a + 27d= 60 ......(i) Now, tn = a + (n – 1) d ∴t28 = a + (28 – 1) d ∴t28 = a + 27d Putting the value of a+ 27d ∴t28 = 60[From (i)] ∴Twenty eighth term of A.P. is 60. |
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