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Mathematics 8 Online
OpenStudy (anonymous):

please help

OpenStudy (anonymous):

OpenStudy (korosh23):

If they are moving up by 0.5 then times 25 by 0.5 and see if you can get the right answer.

OpenStudy (welshfella):

this is an arithmetic series with common difference = 1/2

OpenStudy (anonymous):

what does the S mean

OpenStudy (welshfella):

the sum:- S25 = the sum of 25 terms

OpenStudy (anonymous):

so is their a formula

OpenStudy (welshfella):

yes for an AS Sn = (n/2)[2a + d(n-1)] where n = number of terms , d = common difference and a = first term. so for your question n = 25 , a = 1/2 and d = 1/2

OpenStudy (welshfella):

just plug those values into the formula and work it out

OpenStudy (anonymous):

okay thanks man

OpenStudy (welshfella):

yw

OpenStudy (anonymous):

162.5?

OpenStudy (welshfella):

12.5 [2*0.5 + 0.5(25-1)] = 12.5 * 13 = 162.5

OpenStudy (welshfella):

yep

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