Last weeks test question

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February 3, 2012 at 3:56 pm #367
Avatar of infiniteone
infiniteone

In last week’s test they asked me what is the sum of all the terms in the arithmetic series:

4+8+12+16+20+24+28+32+36+40
February 3, 2012 at 4:01 pm #376
Avatar of kenty
kenty

I don’t know the answer to this.

Sorry.

:(

February 5, 2012 at 11:34 am #377
Avatar of snapster
snapster

First thing you’d do is add them up.

But, if you use the formula for the sum of the terms of an arithmetic series:

S=(n/2)[2a+(n-1)d], where n is the numbers of terms (10), a is the first term (4) and d is the difference between any 2 consecutive terms (4).

Thus, the sum of the above series is:

(10/2)[2x4+(10-1)x4]=220
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