Which of the relations below is a function?

{(red, sign) (yellow, sign) (red, light) (green, light)}

{(blue, bird) (red, car) (yellow, bus) (yellow, taxi)}

{(red, apple) (purple, grape) (yellow, banana) (green, pear)}

Afurniture manufacturer produces chairs and sofas. each chair requires 10 yards of fabric, and each sofa requires 20 yards of fabric. the manufacturer has 300 yards of fabric available. to fulfill orders, the number of sofas must be at least twice the number of chairs. let x be the number of chairs and y the number of sofas. which inequalities are described in the problem? check all of the boxes that apply

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In a class, there are 12 girls. if the ratio of boys to girls is 5: 4 how many boys are there in the class