Difference between revisions of "2005 AMC 8 Problems/Problem 24"

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First we can start at 200 and work our way down we want to do <math>/2</math> the most so if we come across an odd number we just subtract 1.  So <math>200/2</math>=<math>100</math>, <math>100/2</math>=<math>50</math>, <math>50/2</math>=<math>25</math>, <math>25-1</math>=<math>24</math>, <math>24/2</math>=<math>12</math>, <math>12/2</math>=<math>6</math>, <math>6/2</math>=<math>3</math>, <math>3-1</math>=<math>2</math>, and <math>2/2</math>=<math>1</math>.  We made our way back to 1 but since it is the amount of times the button is pressed than the answer should be \boxed{\textbf{(B)}\ 9}$.
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First we can start at 200 and work our way down we want to do <math>/2</math> the most so if we come across an odd number we just subtract 1.  So <math>200/2</math>=<math>100</math>, <math>100/2</math>=<math>50</math>, <math>50/2</math>=<math>25</math>, <math>25-1</math>=<math>24</math>, <math>24/2</math>=<math>12</math>, <math>12/2</math>=<math>6</math>, <math>6/2</math>=<math>3</math>, <math>3-1</math>=<math>2</math>, and <math>2/2</math>=<math>1</math>.  We made our way back to 1 but since it is the amount of times the button is pressed than the answer should be <math>\boxed{\textbf{(B)}\ 9}</math>.
  
 
==See Also==
 
==See Also==
 
{{AMC8 box|year=2005|num-b=23|num-a=25}}
 
{{AMC8 box|year=2005|num-b=23|num-a=25}}
 
{{MAA Notice}}
 
{{MAA Notice}}

Revision as of 15:33, 28 September 2020

Problem

A certain calculator has only two keys [+1] and [x2]. When you press one of the keys, the calculator automatically displays the result. For instance, if the calculator originally displayed "9" and you pressed [+1], it would display "10." If you then pressed [x2], it would display "20." Starting with the display "1," what is the fewest number of keystrokes you would need to reach "200"?

$\textbf{(A)}\ 8\qquad\textbf{(B)}\ 9\qquad\textbf{(C)}\ 10\qquad\textbf{(D)}\ 11\qquad\textbf{(E)}\ 12$

Solution

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First we can start at 200 and work our way down we want to do $/2$ the most so if we come across an odd number we just subtract 1. So $200/2$=$100$, $100/2$=$50$, $50/2$=$25$, $25-1$=$24$, $24/2$=$12$, $12/2$=$6$, $6/2$=$3$, $3-1$=$2$, and $2/2$=$1$. We made our way back to 1 but since it is the amount of times the button is pressed than the answer should be $\boxed{\textbf{(B)}\ 9}$.

See Also

2005 AMC 8 (ProblemsAnswer KeyResources)
Preceded by
Problem 23
Followed by
Problem 25
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
All AJHSME/AMC 8 Problems and Solutions

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