Answer: Choice A
L = 65 - 15d; discrete
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Explanation:
He starts with 65 cm of bread. After the first day he has 65-15 = 50 cm left over. After the second day he has 65-15*2 = 35 cm left over, and so on.
In general, he has 65-15d centimeters left over after d number of days have elapsed. For example, if d = 3 days pass by, then he has 65-15d = 65-15*3 = 65-45 = 20 cm left over.
So that's why the equation we're after is L = 65-15d where d is the number of days, and L is the amount left over in cm.
The number of days is discrete because we're dealing with the set of nonnegative numbers {0,1,2,3,4,...}. We can't have d = 2.5 for instance.
Because the input variable d is discrete, this automatically means L is discrete as well. Consider a finite domain such as {0,1,2,3}. This finite domain would map to the finite range {65,50,35,20}. These two finite sets are sufficient to say we have a discrete function.
A discrete function leads to a discrete graph which is simply a set of points. You would not connect the dots to form a straight line (simply leave the points as separate islands).