Difference between revisions of "2016 AMC 8 Problems/Problem 20"

Latest revision as of 15:32, 7 April 2023

Problem

The least common multiple of $a$ and $b$ is $12$ , and the least common multiple of $b$ and $c$ is $15$ . What is the least possible value of the least common multiple of $a$ and $c$ ?

$\textbf{(A) }20\qquad\textbf{(B) }30\qquad\textbf{(C) }60\qquad\textbf{(D) }120\qquad \textbf{(E) }180$

Solution

We wish to find possible values of $a$ , $b$ , and $c$ . By finding the greatest common factor of $12$ and $15$ , we can find that $b$ is 3. Moving on to $a$ and $c$ , in order to minimize them, we wish to find the least such that the least common multiple of $a$ and $3$ is $12$ , $\rightarrow 4$ . Similarly, with $3$ and $c$ , we obtain $5$ . The least common multiple of $4$ and $5$ is $20 \rightarrow \boxed{\textbf{(A)} 20}$

Video Solution (CREATIVE THINKING + ANALYSIS!!!)

https://youtu.be/_-xC-qQMCbk

~Education, the Study of Everything

Video Solution by OmegaLearn

https://youtu.be/HISL2-N5NVg?t=2340

~ pi_is_3.14

Video Solution

https://youtu.be/7tGFq07njVo

~savannahsolver

2016 AMC 8 (Problems • Answer Key • Resources)
Preceded by Problem 19	Followed by Problem 21
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

The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.

@@ Line 6: / Line 6: @@
 ==Solution==
-We wish to find possible values of <math>a</math>,<math>b</math>, and <math>c</math>. By finding the greatest common factor of <math>12</math> and <math>15</math>, algebraically, it's some multiple of <math>b</math> and from looking at the numbers, we are sure that it is 3, thus <math>b</math> is 3. Moving on to <math>a</math> and <math>c</math>, in order to minimize them, we wish to find the least such that the least common multiple of <math>a</math> and <math>3</math> is <math>12</math>, <math>\rightarrow 4</math>. Similarly with <math>3</math> and <math>c</math>, we obtain <math>5</math>. The least common multiple of <math>4</math> and <math>5</math> is <math>20 \rightarrow \boxed{\textbf{(A)} 20}</math>
+We wish to find possible values of <math>a</math>, <math>b</math>, and <math>c</math>. By finding the greatest common factor of <math>12</math> and <math>15</math>, we can find that <math>b</math> is 3. Moving on to <math>a</math> and <math>c</math>, in order to minimize them, we wish to find the least such that the least common multiple of <math>a</math> and <math>3</math> is <math>12</math>, <math>\rightarrow 4</math>. Similarly, with <math>3</math> and <math>c</math>, we obtain <math>5</math>. The least common multiple of <math>4</math> and <math>5</math> is <math>20 \rightarrow \boxed{\textbf{(A)} 20}</math>
-{{AMC8 box|year=2016|num-b=19|num-a=21}}
-{{MAA Notice}}
+==Video Solution (CREATIVE THINKING + ANALYSIS!!!)==
+https://youtu.be/_-xC-qQMCbk
+~Education, the Study of Everything
-== Video Solution ==
+== Video Solution by OmegaLearn==
 https://youtu.be/HISL2-N5NVg?t=2340
 ~ pi_is_3.14
+== Video Solution ==
+https://youtu.be/7tGFq07njVo
+~savannahsolver
+==See Also==
+{{AMC8 box|year=2016|num-b=19|num-a=21}}
+{{MAA Notice}}

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