Question

A local high school held a two-day fundraiser selling lunches. The equations shown represent the amount of money the school collected during the two days. {12x + 4y = 15232x + 12y = 420 In the equations, x represents the cost of a chicken lunch and y represents the cost of a vegetarian lunch. Which is the cost of the vegetarian lunch?

Answer 1

Answer:

  11

Step-by-step explanation:

The two equations appear to be ...

• 12x +4y = 152
• 32x +12y = 420

These can be solved for y using Cramer's rule:

  y = (152(32) -420(12))/(4(32) -12(12)) = -176/-16 = 11

The cost of the vegetarian lunch is 11.

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Comment on Cramer's Rule

For equations ...

  ax +by =c

  dx +ey = f

The solutions are ...

  x = (bf -ey)/(bd -ea)

  y = (cd -fa)/(bd -ea) . . . . note the denominators are the same expression

Once you memorize the pattern of products, this can be the simplest way to solve a pair of equations--especially if you only need one of the variable values.