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1. A sequence is formed by adding $2$ to the triple of the previous term. If the first term is $1$, how many multiples of $6$ less than $10{,}000$ would be terms of the sequence?

2. Recall that a Fibonacci sequence is one in which all entries from the third onward are the sum of the two entries before it. If the $5$th and $8$th entries of a Fibonacci Sequence are $19$ and $79$, respectively, then what is the first entry of this sequence?

3. We know that $\dfrac{1}{13}=0.0769230769230769230769230769230769\cdots$ When $\dfrac{1}{1300}$ is written as a repeating decimal, what is its $100$th digit to the right of the decimal point?

 Dec 23, 2020
 #1
avatar+26396 
+2

2.

Recall that a Fibonacci sequence is one in which all entries from the third onward are the sum of the two entries before it.
If the 5th and 8th entries of a Fibonacci Sequence are 19 and 79,
respectively, then what is the first entry of this sequence?

 

a5=19a8=79a6+a7=a8(1)a6+a7=79a5+a6=a7(2)19+a6=a7(1)+(2):19+2a6+a7=79+a719+2a6=792a6=79192a6=60|:2a6=30

 

a4+a5=a6a4+19=30a4=11a3+a4=a5a3+11=19a3=8a2+a3=a4a2+8=11a2=3a1+a2=a3a1+3=8a1=5

 

laugh

 Dec 23, 2020
 #3
avatar+130477 
+1

Nice,heureka  !!!!

 

 

cool cool cool

CPhill  Dec 23, 2020
 #4
avatar+26396 
0

Thank you, CPhill ! 

 

laugh

heureka  Dec 24, 2020
 #2
avatar+130477 
+1

1/1300  =  1/13 *  ( 1/100)  =  .00076923

 

The part in red is the repeating part with a period of 6

 

So

 

When  n  = 16

 

2 + 6 (16)  =  2 + 96  = 98 digits  to the right of the decimal point

 

So....the 100th digit will be the second digit in the period  =  7

 

cool cool cool

 Dec 23, 2020

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