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Difference between revisions of "2018 AMC 10A Problems/Problem 3"

(These two solutions are basically the same, so we only need one of them. The second solution explains it better, so I removed the first one.)
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<math>\textbf{(A) }\text{January 2}\qquad\textbf{(B) }\text{January 12}\qquad\textbf{(C) }\text{January 22}\qquad\textbf{(D) }\text{February 11}\qquad\textbf{(E) }\text{February 12}</math>
 
<math>\textbf{(A) }\text{January 2}\qquad\textbf{(B) }\text{January 12}\qquad\textbf{(C) }\text{January 22}\qquad\textbf{(D) }\text{February 11}\qquad\textbf{(E) }\text{February 12}</math>
  
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==Video Solution==
 
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https://youtu.be/bPfLeXu9kx0
 
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Education, the Study of Everything
 
  
 
== Solution ==
 
== Solution ==
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~savannahsolver
 
~savannahsolver
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 +
https://youtu.be/bPfLeXu9kx0
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 +
Education, the Study of Everything
  
 
== See Also ==
 
== See Also ==

Revision as of 17:52, 29 November 2020

Problem

A unit of blood expires after $10!=10\cdot 9 \cdot 8 \cdots 1$ seconds. Yasin donates a unit of blood at noon of January 1. On what day does his unit of blood expire?

$\textbf{(A) }\text{January 2}\qquad\textbf{(B) }\text{January 12}\qquad\textbf{(C) }\text{January 22}\qquad\textbf{(D) }\text{February 11}\qquad\textbf{(E) }\text{February 12}$


Solution

The problem says there are $10! = 10\cdot 9\cdot 8\cdot 7\cdot 6\cdot 5\cdot 4\cdot 3\cdot 2\cdot 1$ seconds. Convert $10!$ seconds to minutes by dividing by $60$: $9\cdot 8\cdot 7\cdot 5\cdot 4\cdot 3\cdot 2$ minutes. Convert minutes to hours by again, dividing by $60$: $9\cdot 8\cdot 7\cdot 2$ hours. Convert hours to days by dividing by $24$: $3\cdot 7\cdot 2 = 42$ days.

Now we need to count $42$ days after January 1. Since we start on Jan. 1, then we can't count that as a day itself. When we reach Jan. 31(The end of the month), we only have counted 30 days. $42 - 30 = 12$. Count $12$ more days, resulting $\fbox{\textbf{(E) }\text{February 12}}$ 

~nosysnow and Max0815

Video Solution

https://youtu.be/vO-ELYmgRI8

https://youtu.be/FbSYTL8tPwo

~savannahsolver

https://youtu.be/bPfLeXu9kx0

Education, the Study of Everything

See Also

2018 AMC 10A (Problems • Answer Key • Resources)
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Problem 2 		Followed by
Problem 4
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All AMC 10 Problems and Solutions

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