Difference between revisions of "2009 AMC 8 Problems/Problem 5"

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List them out, adding the three previous numbers to get the next number,
 
List them out, adding the three previous numbers to get the next number,
  
<cmath>1,2,3,6,11,20,37,\boxed{\textbf{(D)}\ 68}</cmath>
+
1,2,3,6,11,20,37,68
  
 
==Video Solution ==
 
==Video Solution ==

Revision as of 13:14, 14 August 2021

Problem

A sequence of numbers starts with $1$, $2$, and $3$. The fourth number of the sequence is the sum of the previous three numbers in the sequence: $1+2+3=6$. In the same way, every number after the fourth is the sum of the previous three numbers. What is the eighth number in the sequence?

$\textbf{(A)}\  11  \qquad \textbf{(B)}\   20  \qquad \textbf{(C)}\   37  \qquad \textbf{(D)}\   68  \qquad \textbf{(E)}\    99$

Solution

List them out, adding the three previous numbers to get the next number,

1,2,3,6,11,20,37,68

Video Solution

https://youtu.be/USVVURBLaAc?t=221

See Also

2009 AMC 8 (ProblemsAnswer KeyResources)
Preceded by
Problem 4
Followed by
Problem 6
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
All AJHSME/AMC 8 Problems and Solutions

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