Question 152619
First number is x.,
Second number is y.
1.{{{x+y=12}}}
2.{{{x=5y}}}
You can then substitute eq. 2 into eq. 1.
1.{{{x+y=12}}}
{{{5y+y=12}}}
{{{6y=12}}}
{{{y=2}}}
Then from 2,
2.{{{x=5y}}}
{{{x=5(2)}}}
{{{x=10}}}
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The rules for irrational numbers are similar.
Adding or subtracting two irrational numbers gives an irrational number.
Multiplying or dividing irrational numbers can give either rational or irrational numbers.
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Examples: 
{{{sqrt(2)*sqrt(5)=sqrt(10)}}} Irrational number
{{{sqrt(2)*sqrt(2)=2}}} Rational number
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{{{sqrt(6)/sqrt(2)=sqrt(3)}}} Irrational number
{{{sqrt(5)/sqrt(5)=1}}} Rational number