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March 1, 2015

March 1, 2015

Posted by **Jon** on Tuesday, March 4, 2008 at 12:18pm.

Sn=a1(1-r^n)/1-r

189=a1(1-1/2^3)/1-1/2

189=a1(-.5)/.5

189/-.25

a1=-756

- Math -
**Reiny**, Tuesday, March 4, 2008 at 12:57pmYOur third line is wrong

should be:

189 = a(1 - 1/8)/(1 - 1/2)

189 = a(7/8)/(1/2)

189 = a(7/4)

756 = 7a

108 = a

(check 108+54+27 = 189 !)

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