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2 years ago

69. The O'Brien's had $400.0 in a special

Mathematics

1 answer:

LuckyWell [14K]2 years ago

8 0

Hello :D

$40.00 x 3 = $120.00

$20.00 x 2 = $40.00

$120.00 + $40.00 = $160.00

$400.00 - $160.00 = $240.00

There is $240.00 left in the account.

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Find a1, for the arithmetic series<br> with S14 = - 420 and d = -6.

faust18 [17]

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$\bf \textit{sum of a finite arithmetic sequence} \\\\ S_n=\cfrac{n(a_1+a_n)}{2}\qquad \begin{cases} a_n=n^{th}\ term\\ n=\textit{last term's}\\ \qquad position\\ a_1=\textit{first term}\\ \cline{1-1} n= 14\\ S_{14}=-420\\ a_{14}=a_1-78 \end{cases}\implies S_{14}=\cfrac{n(a_1+a_{14})}{2} \\\\\\ -420=\cfrac{14[a_1+(a_1-78)]}{2}\implies -420=7(2a_1-78)\implies \cfrac{-420}{7}=2a_1-78 \\\\\\ -60=2a_1-78\implies 18=2a_1\implies \cfrac{18}{2}=a_1\implies 9=a_1$

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3 years ago

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Answer:

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Step-by-step explanation:

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Answer:

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Step-by-step explanation:

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