2009 AMC 8 Problems/Problem 5

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: $1\plus{}2\plus{}3\equal{}6$ (Error compiling LaTeX. Unknown error_msg). 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?

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

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2009 AMC 8 Problems/Problem 5

Problem