"Index of 3 Test"

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"Index of 3 Test"

by sanju09 » Wed Apr 22, 2009 2:03 am
To verify that a given n-digit positive integer is divisible by 7, we perform the "Index of 3 Test" with the number; for example, to verify that 259 is divisible by 7, following way goes the "Index of 3 Test":

259 → 2 × 3^2 + 5 × 3^1 + 9 × 3^0 = 18 + 15 + 9 = 42. (Step 1)

42 → 4 × 3^1 + 2 × 3^0 = 12 + 2 = 14. (Step 2)

14 → 1 × 3^1 + 4 × 3^0 = 3 + 4 = 7. (Step 3)

It took 3 such steps to get 7 in the end, and we’re sure that 259 is divisible by 7. How many such steps are needed to be taken so as to make sure that 11116 is divisible by 7?
A. 2
B. 3
C. 4
D. 5
E. 6


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by Sher1 » Wed Apr 22, 2009 4:35 am
3 steps

11116 with the method gives you 126 then 21 and then 7

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by shibal » Thu Apr 23, 2009 10:52 am
i didn't get the method... could someone explaine pls?

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by gmat740 » Thu Apr 23, 2009 12:15 pm
Hello Sanju,
May I know the source of the Questions you are putting up here?
I hope you don't mind this.