ps 13

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ps 13

by dunkin77 » Tue Jun 19, 2007 3:03 pm
Can anyone help? OA is A.
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by givemeanid » Tue Jun 19, 2007 3:49 pm
an = 2a(n-1) - x
a5 = 2a4 - x

Now, a4 = 2a3 -x

So, a5 = 2(2a3 - x) - x
99 = 2(2 * 27 - x) - x
99 = 108 - 2x - x
3x = 9
x = 3