Question

Find the sum of the first 35 terms of the following series, to the nearest integer. 3, 11, 19...

Answer 1

Answer:   4865

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Explanation:

The sequence {3,11,19,...} is arithmetic since we are adding 8 to each term to get the next one

• 3+8 = 11
• 11+8 = 19

etc. This means the common difference is d = 8.

The first term is a = 3

Let's use this formula

S = n*(2*a + d(n - 1) )/2

so we can find the sum of the first n terms. In this case, n = 35

So,

S = n*(2*a + d(n - 1) )/2

S = 35*(2*3 + 8(35 - 1) )/2

S = 35*(6 + 8(34))/2

S = 35*(6 + 272)/2

S = 35*(278)/2

S = 35*139

S = 4865