Difference between revisions of "2009 Grade 8 CEMC Gauss Problems/Problem 5"

(Created page with "==Problem== Rounded to <math>2</math> decimal places, <math>\frac79</math> is <math> \text{ (A) }\ 0.70 \qquad\text{ (B) }\ 0.77 \qquad\text{ (C) }\ 0.78 \qquad\text{ (D) }\...")
 
(Replaced content with "{{delete|page moved}}")
(Tag: Replaced)
 
Line 1: Line 1:
==Problem==
+
{{delete|page moved}}
Rounded to <math>2</math> decimal places, <math>\frac79</math> is
 
 
 
<math> \text{ (A) }\ 0.70 \qquad\text{ (B) }\ 0.77 \qquad\text{ (C) }\ 0.78 \qquad\text{ (D) }\ 0.79 \qquad\text{ (E) }\ 0.80 </math>
 
==Solution==
 
We can use the fact that <math>\frac79 = 0.\overline{777}</math>.
 
 
 
Rounding this number to the nearest hundredth (to <math>2</math> decimal places), we get <math>\boxed {\textbf {(C) } 0.78}</math> because the thousandths place is greater than or equal to <math>5</math>, so it is closer to <math>0.78</math> than <math>0.77</math>.
 
 
 
~anabel.disher
 
==Solution 2 (answer choices)==
 
We can go backwards by multiplying answer choices by <math>9</math> and seeing how they compare to <math>7</math>
 
 
 
Multiplying <math>0.78</math> by <math>9</math>, we get:
 
 
 
<math>0.78 \times 9 = 7.02</math>
 
 
 
This makes <math>0.79</math> and <math>0.80</math> too large and <math>0.70</math> too small, eliminating them as answers
 
 
 
<math>0.77 \times 9 = 6.93</math>
 
 
 
We can now look at which answer <math>7</math> is closest to, using the distance to <math>7</math>:
 
 
 
<math>7 - 6.93 = 0.07</math>
 
 
 
<math>7.02 - 7 = 0.02</math>
 
 
 
<math>7.02</math> is closer to <math>7</math>, so the answer is <math>\boxed {\textbf {(C) } 0.78}</math>
 
 
 
~anabel.disher
 

Latest revision as of 12:15, 1 October 2025

This page has been proposed for deletion. Reason: page moved


Note to sysops: Before deleting, please review: • What links hereDiscussion pageEdit history