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3 years ago

I NEED HELP QUICKLY!!! What is the sum of the first 140 positive multiples of 3?

Mathematics

1 answer:

garri49 [273]3 years ago

5 0

Answer:

Step-by-step explanation:

The multiples of 3 are

3, 6, 9, 12, 15, ...........

The terms form an arithmetic sequence with common difference of 3.

The sum to n terms is

$S_{n}$ = $\frac{n}{2}$ [2a₁ + (n - 1)d ]

where a₁ is the first term and d the common difference

Here a₁ = 3 and d = 3, thus

$S_{140}$ = $\frac{140}{2}$ [ (2 × 3) + (139 × 3) ]

= 70(6 + 417) ] = 70 × 423 = 29610 → C

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