Roast beef has 25g of protein and 11g of calcium per serving. a serving of mashed potatoes has 2g of calcium and 25g of calcium. how many servings of each are needed to supply exactly 25g of protein and 61g of calcium?

Let R and M be the numbers of serving of roast beef and mashed potato.

25R     +    2M      =   29   >  1

11R      +     25M      =     61 >    2

From (1): 2R   =   29    -    25M

or     M   =     29/2     - 25/2 R

Substitute this into (2):

11R      +      25(29/2     -     25/2 M)     =     61

11R      +       362.5      -       312.5R     =     61

301.5      =       301.5R

R      =        1

Using    R     =     1, we can get

11(1)      +     25M     =      61

25M       =      50

M         =           2

Therefore, you will need ONE SERVING  of Roast Beef and TWO SERVINGS of Mash Potatoes.

Hope that helps                                                : )