# Difference between revisions of "2001 AMC 10 Problems/Problem 7"

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<math> \frac{x}{10000}=\frac{4}{x} </math> | <math> \frac{x}{10000}=\frac{4}{x} </math> | ||

− | Cross-multiply and solve for x. | + | Cross-multiply and solve for <math> x </math>. |

<math> x^2=40000 \implies x=200 </math>. | <math> x^2=40000 \implies x=200 </math>. | ||

− | + | <math> 200/10000=2/100= \boxed{\textbf{(C) }0.02} </math>. |

## Revision as of 15:03, 16 March 2011

## Problem

When the decimal point of a certain positive decimal number is moved four places to the right, the new number is four times the reciprocal of the original number. What is the original number?

## Solution

We can write our equation as:

Cross-multiply and solve for .

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