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3 years ago

What is the sum of the last four terms of the series 7+9+11+...21

Mathematics

1 answer:

Sidana [21]3 years ago

8 0

For sake of convenience, reverse the series, then it would be:

21,19,17.....7

a=21, d = -2,

s(4) = 4/2 (21+15)

s(4)=2(36)

s(4) = 72

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to solve this we need to translate into math terms, so

Step 1

a) let d represents the number of dimes

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re write the expressions

$\begin{gathered} number\text{ of dimes=d} \\ seven\text{ times the number of dimes = 7d} \\ \end{gathered}$

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