x+y=21 y=6x

Question

X+y=21 y=6x

Answer 1

This is a SYSTEM OF EQUATIONS.  The easiest way to solve this one is probably to use SUBSTITUTION.

 

You know that y=6x, so substitute 6x for y in the first equation, and solve for the value of x:

 

x  +  y  =  21

 

x  +  6x =  21

 

    7x     =  21

 

    7x/7  =  21/7

   

      x     =   3

 

So far so good?  Now we can calculate the value of y by substituting again, this time 3 for x in the second equation:

 

      y  =  6x

 

      y  =  6(3)

 

      y  =  18

 

Now you know the values of both x and y.  Lets check to make sure we are correct:

 

  3  +  18  =  21  ok!

 

     18   =  6(3)    ok!

 

Make sure you show your solution as an ORDERED PAIR in the (x, y) format:

 

  (3, 18)

 

 

 

Answer 2

Since you have two variables, you need to figure out how to get down to 1 variable. This is done by replacing the y in the equation. Replace the y with 6x since y=6x.  The equation becomes x + 6x = 21. This becomes 7x=21. Divide both sides by 7. x=3