Andy C. answered • 10/30/17

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Cost ( x , y) = 3.50x + 5y where x is the number of small candles and y is the number of large candles

x+y >=20

Cost(x,y)<=80

y >= 20 - x

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y = 20 -x vs. 80 = 3.5x + 5y

80 = 3.5x + 5( 20 - x)

80 = 3.5x + 100 - 5x

80 = 100 - 1.5x

-20 = -1.5x

-200 = -15x

x = 200/15 = 40/3

y = 20 - 40/3 = 20 = 13 and 1/3 = 6 and 2/3

THe lines intersect at ( 13 and 1/3 , 6 and 2/3)

(40/3)*3.5 + 5 * (20/3) = (40/3)(7/2) + 5 * (20/3) = 280/6 + 100/3 = 280/6 + 200/6 = 480/6 = 80

So 13 and 1/3 small candles and 6 and 2/3 large candles costs exactly $80

She can buy 14 small candles and 6 large candles for $79

She can buy 15 small candles and 5 large candles for $77.50

She can buy 16 small candles and 4 large candles for $76

She can buy 17 small candles and 3 large candles for $74.50

She can buy 18 small candles and 2 large candles for $73

She can buy 19 small candles and 1 large candles for $71.50

She can buy 20 small candles for $70

Jessica H.

10/30/17