Art of Problem Solving

2016 AMC 10A Problems/Problem 2

Problem

For what value of $x$ does $10^{x}\cdot 100^{2x}=1000^{5}$?

$\textbf{(A)}\ 1 \qquad\textbf{(B)}\ 2\qquad\textbf{(C)}\ 3\qquad\textbf{(D)}\ 4\qquad\textbf{(E)}\ 5$

Solution

We can rewrite $10^{x}\cdot 100^{2x}=1000^{5}$ as $10^{5x}=10^{15}$. Since the bases are equal, we can set the exponents equal: $5x=15$. Solving gives us: \[x = \boxed{\textbf{(C)}\;3.}\]