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# evaluating an arithmetic series watch

1. ok the question is
n
∑ (4- r/2)
6

so the terms are are 1 + 0.5 + 0 -0.5 ......4-n/2

so i tried to evaluate it

1 + 4-n/2= 5-n/2

then multiply by no. of pairs n/2

5-n/2 x n/2 = 10-n

i thought that would be right

how?
2. need an asap anyone please...its bugging me
3. The number of pairs isn't n/2, because you're starting at 6, so it's (n-5)/2. Still not sure how you get the answer though.
4. (Original post by Libertine)
The number of pairs isn't n/2, because you're starting at 6, so it's (n-5)/2. Still not sure how you get the answer though.
thanx

ive got it to 1/2 (n-5)(10-n)

but dont know where they 1/4 came from!?! this is frustrating
5. (5-n/2) x (n-5)/2

= (5n-25)/2 - (n²-5n)/4

= (10n - 50)/4 - (n²-5n)/4

= (15n - n² - 50)/4

= (1/4) x (n-5)(10-n)
6. (Original post by Libertine)
(5-n/2) x (n-5)/2

= (5n-25)/2 - (n²-5n)/4

= (10n - 50)/4 - (n²-5n)/4

= (15n - n² - 50)/4

= (1/4) x (n-5)(10-n)
thank you soo much

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