Difference between revisions of "2012 AMC 8 Problems/Problem 13"
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Jamar bought some pencils costing more than a penny each at the school bookstore and paid <math> | Jamar bought some pencils costing more than a penny each at the school bookstore and paid <math> | ||
\textdollar 1.43 </math>. Sharona bought some of the same pencils and paid <math> \textdollar 1.87 </math>. How many more pencils did Sharona buy than Jamar? | \textdollar 1.43 </math>. Sharona bought some of the same pencils and paid <math> \textdollar 1.87 </math>. How many more pencils did Sharona buy than Jamar? | ||
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We find the difference between <math>1.43</math> and <math>1.87</math> is <math> 1.87-1.43 = 0.44 </math>, which is the extra cost of Sharona's pencils than Jamar's pencils. Because the difference between the amounts of the pencils they bought must be divided evenly by <math>0.44</math>, looking into the answers, <math>2</math> or <math>4</math> is possibly correct. It gives us the price of each pencil should be <math> 0.44/2=0.22 </math> or <math> 0.44/4=0.11 </math>, respectively. Then we find only <math>0.11</math> can be divided evenly by <math>1.43</math> and <math>1.87</math>. So the answer is <math> \boxed{\textbf{(C)}\ 4} </math> | We find the difference between <math>1.43</math> and <math>1.87</math> is <math> 1.87-1.43 = 0.44 </math>, which is the extra cost of Sharona's pencils than Jamar's pencils. Because the difference between the amounts of the pencils they bought must be divided evenly by <math>0.44</math>, looking into the answers, <math>2</math> or <math>4</math> is possibly correct. It gives us the price of each pencil should be <math> 0.44/2=0.22 </math> or <math> 0.44/4=0.11 </math>, respectively. Then we find only <math>0.11</math> can be divided evenly by <math>1.43</math> and <math>1.87</math>. So the answer is <math> \boxed{\textbf{(C)}\ 4} </math> | ||
− | == | + | ==Solution 3 (quick solution)== |
− | + | You can quickly tell, if you have memorized your times tables, that <math>187</math> and <math>143</math> are both multiples of <math>11</math>. Additionally, the difference is 44 cents. That means that there are <math> \boxed{\textbf{(C)}\ 4} </math> more pencils purchased by Sharona because <math>11*4 = 44</math>. | |
==See Also== | ==See Also== | ||
{{AMC8 box|year=2012|num-b=12|num-a=14}} | {{AMC8 box|year=2012|num-b=12|num-a=14}} | ||
{{MAA Notice}} | {{MAA Notice}} |
Latest revision as of 15:36, 28 December 2023
Problem 13
Jamar bought some pencils costing more than a penny each at the school bookstore and paid . Sharona bought some of the same pencils and paid
. How many more pencils did Sharona buy than Jamar?
Solution 1
We assume that the price of the pencils remains constant. Convert and
to cents. Since the price of the pencils is more than one penny, we can find the price of one pencil (in cents) by taking the greatest common divisor of
and
, which is
. Therefore, Jamar bought
pencils and Sharona bought
pencils. Thus, Sharona bought
more pencils than Jamar.
Solution 2
We find the difference between and
is
, which is the extra cost of Sharona's pencils than Jamar's pencils. Because the difference between the amounts of the pencils they bought must be divided evenly by
, looking into the answers,
or
is possibly correct. It gives us the price of each pencil should be
or
, respectively. Then we find only
can be divided evenly by
and
. So the answer is
Solution 3 (quick solution)
You can quickly tell, if you have memorized your times tables, that and
are both multiples of
. Additionally, the difference is 44 cents. That means that there are
more pencils purchased by Sharona because
.
See Also
2012 AMC 8 (Problems • Answer Key • Resources) | ||
Preceded by Problem 12 |
Followed by Problem 14 | |
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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