Week15-Applications of Rational Equations

This week we learned how to solve the unknown value from the score formula

For example:

\frac{2}{v}\frac{5}{4v}=3

Then we make all the term time common denominator

so we get the common denominator is 4v

8-5=12v

12v=3

v=0.25

Then we learn how to solve the unknow number in the life things

This is the one of the example
we get Mary’s apprentice need 9 hours long to build a deck than it takes Marcy

So we make Mary need x hours to finish , her apprentice need x+9 hours to finish

And if they do together , so they will finish in 20 hours

so we know after 1 hour Mary finished\frac{1}{x} , her apprentice finished \frac{ 1 }{x+9}

so we got a function that are after 20 hours

\frac{20}{x}+\frac{20}{x+9}=1(this ‘1’ is mean 20 over 20)

And you use the way that times common denominator

we got x^2 -31x-180=0

then we factor

we get (x-36)(x+5)=0

And we get 36 ,-5

but -5 is not belong to the question

so we just get 36 is mary

than we get 36+9=45 is her apprentice

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