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by Anurag@Gurome » Fri Nov 04, 2011 10:41 pm
jainrahul1985 wrote:In an arithmetic progression a1 = 250 , a17=130 . What is a24 ?

A. 100 B. 85.5 C. 77.5 D. 65 E. 50

OA C
nth term of the sequence is given by an = a1 + (n - 1)d, where a1 is the 1st term and d is the common difference.
a17 = 250 + (17 - 1)d = 130 or 16d = -120 or d = -15/2
a24 = 250 + (24 - 1)d or a24 = 250 + 23(-15/2) = 250 - 172.5 = 77.5

The correct answer is C.
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by LalaB » Sat Nov 05, 2011 12:51 am
a17=a1+d(17-1)
130=250+16d
d=-15/2

since the gap between a24 and a17 is 7 (24-17), then a17+7d=a24 or
130+7*(-15/2)=77.5
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by gmatblood » Sat Nov 05, 2011 1:21 am
Do GMAT have a.p questions??!!, at least not directly as this one!
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