# 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