word problem

Question

Roast beef has 25g of protein and 11g of calcium. Mashe potatoes have 2g of protein and 25g of calcium. How many servings each are needed to have 29g of protein and 61g of calcium? (I know the answer, but i don't know how to set it up.)

Answer 1

let x=# of portions of roast beef

let y=# of portions of potatoes

 

25x+2y=29

11x+25y=61

multiply the first equation by 25

25(25x)+25(2y)=25(29

625x+50y=725

multiply the second equation by 2

2(11x)+2(25y)=2(61)

22x+50y=122

now we have...

   625x+50y=725

-    22x+50y=122

_________________

   603x+0=603

   603x=603

         x=1 serving of roast beef

substitute x=1 into either of the original equations

25(1)+2y=29

25+2y=29

2y=4

y=2 servings of potatoes

or...

11(1)+25y=61

11+25y=61

25y=50

y=2 again