SOLUTION: Solve by the elimination method 0.05x+0.25y=11 0.15x+0.05y=12

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Question 145815: Solve by the elimination method

0.05x+0.25y=11
0.15x+0.05y=12

Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
0.05x%2B0.25y=11 Start with the first equation


100%280.05x%2B0.25y%29=100%2811%29 Multiply both side by 100 to move the decimal point 2 places to the right



5x%2B25y=1100 Distribute and multiply.



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0.15x%2B0.05y=12 Start with the second equation


100%280.15x%2B0.05y%29=100%2812%29 Multiply both side by 100 to move the decimal point 2 places to the right



15x%2B5y=1200 Distribute and multiply.







So we now have the system of equations:

system%285x%2B25y=1100%2C15x%2B5y=1200%29



Now in order to solve this system by using elimination/addition, we need to solve (or isolate) one variable. I'm going to solve for y.





In order to solve for one variable, we must eliminate the other variable. So if we wanted to solve for y, we would have to eliminate x (or vice versa).


So lets eliminate x. In order to do that, we need to have both x coefficients that are equal in magnitude but have opposite signs (for instance 2 and -2 are equal in magnitude but have opposite signs). This way they will add to zero. By adding to zero, they can be eliminated.



So to make the x coefficients equal in magnitude but opposite in sign, we need to multiply both x coefficients by some number to get them to an common number. So if we wanted to get 5 and 15 to some equal number, we could try to get them to the LCM.



Since the LCM of 5 and 15 is 15, we need to multiply both sides of the top equation by 3 and multiply both sides of the bottom equation by -1 like this:




3%285x%2B25y%29=3%281100%29 Multiply the top equation (both sides) by 3
-1%2815x%2B5y%29=-1%281200%29 Multiply the bottom equation (both sides) by -1




Distribute and multiply

15x%2B75y=3300
-15x-5y=-1200


Now add the equations together. In order to add 2 equations, group like terms and combine them

%2815x-15x%29%2B%2875y-5y%29=3300-1200

Combine like terms and simplify



cross%2815x-15x%29%2B70y=2100 Notice how the x terms cancel out




70y=2100 Simplify




y=2100%2F70 Divide both sides by 70 to isolate y




y=30 Reduce



Now plug this answer into the top equation 5x%2B25y=1100 to solve for x

5x%2B25y=1100 Start with the first equation



5x%2B25%2830%29=1100 Plug in y=30




5x%2B750=1100 Multiply



5x=1100-750Subtract 750 from both sides


5x=350 Combine like terms on the right side


x=%28350%29%2F%285%29 Divide both sides by 5 to isolate x



x=70 Divide




So our answer is
x=70 and y=30



which forms the ordered pair