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35th term

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35th term

by hey_thr67 » Fri Jun 08, 2012 8:52 am
The first three terms of a sequence are 2,7 and 22. After the first term, each consecutive term can be obtained by multiplying the previous term by 3 and then adding 1. If the sequence continues to be explained, what will be the sum of the tens digit and the unit digit of the 35th term in the sequence ?

A: 2
B: 4
C: 7
D: 9
E: 13


[spoiler]OA is B. How to approach this types of questions ? [/spoiler]
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by dimochka » Fri Jun 08, 2012 9:06 am
Hi,

One way to approach these questions is to look for a recurring pattern by testing the first few terms.

(1) 2
(2) 2*3+1 = 7
(3) 7*3+1 = 22
(4) 22*3+1 = 67

You should already see the pattern in the units digits - it interchanges between 2 and 7.

(5) 67*3+1 = 202

We can stop here. Since we only care about the units and tens digit, the 200 part of the 202 does not matter, because it will only affect higher digits of the number. So realistically you're now back to working with the number 2, and you can see that the tens digit pattern is 0,0,2,6.

The units digit of the 35th number is thus 2, and the tens digit is also 2.
Answer is B.
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