We use cookies to personalise content and advertisements and to analyse access to our website. Furthermore, our partners for online advertising receive pseudonymised information about your use of our website. cookie policy and privacy policy.
 
+0  
 
0
413
3
avatar+564 

I solved this earlier but Im not sure if Im doing it right. Could someone help guide me through this?

 

Solve for y:

 

\(x = 7y\)

\(x+y+z=80\)

\(2x-y+z=105\)

 Mar 2, 2016

Best Answer 

 #1
avatar+2592 
+5

x=7y

x+y+z=80

2x-y+z=105

Isolate and substitute

 

(7y)+y+z=80

8y+z=80

z=80-8y

 

2(7y)+y+(80-8y)=105

14y+y-8y=25

15y-8y=25

7y=25

y=25/7

 Mar 2, 2016
 #1
avatar+2592 
+5
Best Answer

x=7y

x+y+z=80

2x-y+z=105

Isolate and substitute

 

(7y)+y+z=80

8y+z=80

z=80-8y

 

2(7y)+y+(80-8y)=105

14y+y-8y=25

15y-8y=25

7y=25

y=25/7

SpawnofAngel Mar 2, 2016
 #2
avatar+101360 
+5

x = 7y

x + y + z = 80

2x - y + z = 105  →  z  = 105 - 2x + y     (3)

 

Subbing the first equation into the second, we have

 

7y + y + z  = 80   →  8y + z = 80      (4)

 

And subbing the first into (3) we have

 

z = 105 - 2(7y) + y

 

z = 105 - 13y      (5)

 

Put (5)  into (4)

 

8y + 105 - 13y  = 80

 

-5y  = -25    →  y =  5

 

And  z = 105 - 13(5)  = 105 - 65  = 40

 

And x = 7y = 7(5)  = 35

 

So (x, y, z)  = (35, 5, 40)

 

 

 

cool cool cool

 Mar 2, 2016
 #3
avatar+564 
0

Thanks both of you!

 Mar 2, 2016

13 Online Users

avatar
avatar