2001 AMC 8 Problems/Problem 12

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Problem

If $a\otimes b = \dfrac{a + b}{a - b}$, then $(6\otimes 4)\otimes 3 =$

$\text{(A)}\ 4 \qquad \text{(B)}\ 13 \qquad \text{(C)}\ 15 \qquad \text{(D)}\ 30 \qquad \text{(E)}\ 72$

Solution

$6\otimes4=\frac{6+4}{6-4}=5$. $5\otimes3=\frac{5+3}{5-3}=4, \boxed{\text{A}}$

See Also

2001 AMC 8 (ProblemsAnswer KeyResources)
Preceded by
Problem 11
Followed by
Problem 13
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All AJHSME/AMC 8 Problems and Solutions

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