Question

Sum of first 55 terms in an A.P. is 3300, find its 28th term.

Answer 1

Sol. S55 = 3300 [Given]

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)

Answer 2

Hi friend

Here is your Answer
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 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.

Hope it's helpful ✌✌