Mat 220 Week 2

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40. What does it mean if two quantities vary directly? When two quantities vary directly, this means that when one variable is either reduced or increased the other will vary to the same degree. For example if one is tripled, so is the other. 41. In your own words, explain how to solve a variation problem. The first step in solving a variation problem is to make an equation from the problem at hand. The second step would be to take out the values from the statement and enter them into the appropriate spots in the equation and solve for k. Then input that value into the equation and solve the original problems. 42. What does it mean if two quantities vary inversely? To vary inversely means as one variable goes up the other would go down and vice versa. 43. Explain what is meant by combined variation. Give an example with your explanation. When both variations occur in the same equation. 44. Explain what is meant by joint variation. Give an example with your explanation. When a variation is dependent and varies directly upon the product of two other variables In Exercises 45–46, describe in words the variation shown by the given equation. 45. z =k1x 46. z=kx21y 47. We have seen that the daily number of phone calls between two cities varies jointly as their populations and inversely as the square of the distance between them. This model, used by telecommunication companies to estimate the line capacities needed among various cities, is called the gravity model. Compare the model to Newton’s formula for gravitation on page 400 and describe why the name gravity model is

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