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Question

Question: If the sum of the first ten terms of the series is (13/5) + (13/5) + (13/5) + 4 + (13/5) +…, is (16/...

If the sum of the first ten terms of the series is (13/5) + (13/5) + (13/5) + 4 + (13/5) +…, is (16/5)m, then m is equal to:

Answer

Given the ambiguity of the question, and assuming it refers to a similar series pattern as in the related problem, m = 101.

Explanation

Solution

The original question is ambiguous and likely contains a typo. The phrasing "If the sum of the first ten terms of the series is (13/5) + (13/5) + (13/5) + 4 + (13/5) +…, is (16/5)m" has two "is" clauses, leading to confusion and an undefined series.

Assuming the question intended to represent a series similar to the one in the related problem:

(135)2+(225)2+(315)2+42+(445)2+....\left(1 \frac{3}{5}\right)^{2} + \left(2 \frac{2}{5}\right)^{2} + \left(3 \frac{1}{5}\right)^{2} + 4^{2} + \left(4 \frac{4}{5}\right)^{2} + ....

Which can be written as:

(85)2+(125)2+(165)2+(205)2+(245)2+....\left(\frac{8}{5}\right)^{2} + \left(\frac{12}{5}\right)^{2} + \left(\frac{16}{5}\right)^{2} + \left(\frac{20}{5}\right)^{2} + \left(\frac{24}{5}\right)^{2} + ....

The general term can be represented as (4(n+1)5)2\left(\frac{4(n+1)}{5}\right)^2.

The sum of the first 10 terms is:

S10=n=110(4(n+1)5)2=1625n=110(n+1)2S_{10} = \sum_{n=1}^{10} \left(\frac{4(n+1)}{5}\right)^2 = \frac{16}{25} \sum_{n=1}^{10} (n+1)^2

Let k=n+1k = n+1, then:

S10=1625k=211k2S_{10} = \frac{16}{25} \sum_{k=2}^{11} k^2

Using the formula for the sum of squares: k=1Nk2=N(N+1)(2N+1)6\sum_{k=1}^{N} k^2 = \frac{N(N+1)(2N+1)}{6}

k=211k2=(k=111k2)12=11×12×2361=5061=505\sum_{k=2}^{11} k^2 = \left(\sum_{k=1}^{11} k^2\right) - 1^2 = \frac{11 \times 12 \times 23}{6} - 1 = 506 - 1 = 505

Therefore:

S10=1625×505S_{10} = \frac{16}{25} \times 505

Given S10=165mS_{10} = \frac{16}{5}m:

1625×505=165m\frac{16}{25} \times 505 = \frac{16}{5}m

Solving for mm:

m=5055=101m = \frac{505}{5} = 101

Thus, m=101m = 101.