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12 is 15% of what number?

mathkiller  May 22, 2017
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 #1
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12 is 15% of what number?

 

Let the number =N, then:

15%N = 12

0.15N = 12    divide both sides by 0.15

N =12 / 0.15

N = 80

Guest May 22, 2017
 #2
avatar+1493 
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12 is 15% of 80.

 

Setup a proportion. Setting up a proportion allows the calculation to be simpler arithmetically:

 

\(\frac{12}{x}=\frac{15}{100}\)Simplify the 15/100 by dividing the numerator and denominator by the GCF, 5.

\(\frac{12}{x}=\frac{3}{20}\)Cross multiply and solve for x

\(12*20=3x\)Simplify the left hand side of the equation

\(240=3x\) Divide by 3 on bioth sides to isolate x

\(80=x\)

TheXSquaredFactor  May 22, 2017
 #3
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Both of these solutions are essentially doing the same thing 

15% is .15 and as a fraction that 15/100 or 3/20 so by dividing by .15 you are basically multiplying by 20 and dividing by 3.

 

smiley 

JonathanB  May 22, 2017

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