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experts plz help

by runzun » Fri Dec 02, 2011 9:11 am
the infinite sequence a1, a2....an is such that a1 = 7,a2 =8, a3 =10 and an =a_(n-3)+7 for values of n>3. what is the remainder when an is divided by 7?

a)n is the multiple of 3..
b)n is an even no..


oa after some discussion

source : veritas prep test
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Source: — Data Sufficiency |
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by shankar.ashwin » Fri Dec 02, 2011 9:33 am
Statement 1

Given a3 = 10 - Remainder 3

a6 = a3+7 = 17 - Remainder 3

a9 = a6 + 7 = 24 - Remainder 3 (You add a multiple of 7, remainder does not change)


Sufficient.

Statement 2

Given a2 = 8 - Remainder 1

Now we have already calculated a6 (even no) previously and got a different remainder (3)

SO different results - Insuff

A IMO
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by amit2k9 » Mon Dec 05, 2011 3:43 am
a1,a2,a3 = 7,8,10
a4,a5,a6= 14,15,17

a. a3 and a6 have 10 and 15. meaning remainder = 3. sufficient.

b a2,a4 have remainders 1 and 0. hence not sufficient.

A it is.
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