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rebelchick777 Group Title

I need some help please. Write a function rule to describe each statement... the cost in dollars of printing dollar bills when it costs 3.8cents to print a dollar bill. the amount of money you earn mowing lawns at $15 per lawn. the profit you make selling flowers at $1.50 each when each flower costs you $.80

  • one year ago
  • one year ago

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  1. tjones89 Group Title
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    it costs 3.8 cents to print 1 dollar its costs 2 times 3.8 cents to print two dollars it costs 3 times 3.8 cents to print 3 dollars you can see a pattern here right?

    • one year ago
  2. rebelchick777 Group Title
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    yeah,but how do i write them as function rules?

    • one year ago
  3. tjones89 Group Title
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    we use variables! there should be two of them; one will represent the number of dollars, lets call that x and the other will represent the cost to print them, lets call that y

    • one year ago
  4. rebelchick777 Group Title
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    my teacher told me to write the functions as f(x)=...

    • one year ago
  5. tjones89 Group Title
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    ok lets use f(x) instead of y so the cost to print, f(x), should equal the number of dollars, x, times 3.8 cents

    • one year ago
  6. rebelchick777 Group Title
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    so f(x)=3.8x

    • one year ago
  7. tjones89 Group Title
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    yes

    • one year ago
  8. rebelchick777 Group Title
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    ok so then for the second one would it be... f(x)=$15x

    • one year ago
  9. tjones89 Group Title
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    yep

    • one year ago
  10. tjones89 Group Title
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    but actually I made a mistake on the first one

    • one year ago
  11. rebelchick777 Group Title
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    I d dont understand how to write the third one though.

    • one year ago
  12. tjones89 Group Title
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    the function for the first part should give us the cost in dollars, with f(x) = 3.8x we'll end up with the number of cents

    • one year ago
  13. tjones89 Group Title
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    so you just convert 3.8 cents into dollars which should be .038

    • one year ago
  14. rebelchick777 Group Title
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    the profit you make selling flowers at $1.50 each when each flower costs you $.80

    • one year ago
  15. tjones89 Group Title
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    what is the profit if I sell one flower?

    • one year ago
  16. rebelchick777 Group Title
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    70 cents

    • one year ago
  17. tjones89 Group Title
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    right.. and if i sell two flowers?

    • one year ago
  18. rebelchick777 Group Title
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    a dollar and 40 cents

    • one year ago
  19. tjones89 Group Title
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    which is the same as 2 times 70 cents right? if I sell 3 flowers the profit would be 3 times 70 cents and if I sell x flowers the profit will be x times 70 cents

    • one year ago
  20. rebelchick777 Group Title
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    ok so... would the function be f(x)=.70x?

    • one year ago
  21. tjones89 Group Title
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    yes! good job

    • one year ago
  22. rebelchick777 Group Title
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    Thanks. Now i have another question i have this equation... f(x)=$0.59x where x+number of pounds. if i had $10 to buy that turkey how big a turkey could i buy?

    • one year ago
  23. tjones89 Group Title
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    you have f(x) = $0.59x which in words is, the cost of a turkey, f(x), is the number of pounds, x, times 59 cents

    • one year ago
  24. tjones89 Group Title
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    so the cost of a turkey is a function of the number of pounds that it weighs, does that make sense so far?

    • one year ago
  25. rebelchick777 Group Title
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    yeah. i was wondering where you d plug in the $10.

    • one year ago
  26. tjones89 Group Title
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    the ten dollars goes where dollars is represented in the equation

    • one year ago
  27. tjones89 Group Title
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    x is pounds f(x) is dollars so the equation, when we put in 10 dollars, becomes $10 = $0.59x

    • one year ago
  28. tjones89 Group Title
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    and by solving for x you will have found out how big a turkey you could by with 10 dollars

    • one year ago
  29. tjones89 Group Title
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    does that make sense?

    • one year ago
  30. rebelchick777 Group Title
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    16.95lb. is what i got. Yeah it does make sense.

    • one year ago
  31. rebelchick777 Group Title
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    |dw:1350441039671:dw|

    • one year ago
  32. rebelchick777 Group Title
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    |dw:1350441111447:dw|

    • one year ago
  33. rebelchick777 Group Title
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    i dont see the rule for either of these. It says to write a function rule. By the way.. they are two seperate questions.

    • one year ago
  34. tjones89 Group Title
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    ok lets start with the top one we need to find a way to relate x and y in other words we need to be able to describe how much y changes when x changes we can do this with a function y = x times (some number)

    • one year ago
  35. rebelchick777 Group Title
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    i know that,but idk what number it should be.,

    • one year ago
  36. tjones89 Group Title
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    we can find out what number it is by calculating the slope between the points that are given

    • one year ago
  37. tjones89 Group Title
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    with m = (y2-y1)/(x2-x1)

    • one year ago
  38. rebelchick777 Group Title
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    ok. so what should i get?

    • one year ago
  39. tjones89 Group Title
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    lets use the points: (0,1) and (1,3) m = (3-1)/(1-0) = 2

    • one year ago
  40. rebelchick777 Group Title
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    i understand it for the second table the answer would be f(x)=-4.5x. But i still dont see a pattern in the first one.

    • one year ago
  41. tjones89 Group Title
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    maybe graphing the points and seeing them line up would help

    • one year ago
  42. rebelchick777 Group Title
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    the y's are going up by two except for the last one.

    • one year ago
  43. tjones89 Group Title
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    because its a negative x in the last one, if it were positive 3 then y would be 7

    • one year ago
  44. tjones89 Group Title
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    |dw:1350442466454:dw|

    • one year ago
  45. tjones89 Group Title
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    thats the pattern if we follow the negative x points

    • one year ago
  46. tjones89 Group Title
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    the reason it isnt as easy to see as the second problem is because this function will have the form y = mx + b

    • one year ago
  47. tjones89 Group Title
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    whereas the second one was just y = mx

    • one year ago
  48. rebelchick777 Group Title
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    ok so whats the function rule.

    • one year ago
  49. tjones89 Group Title
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    well we're using y = mx + b as the template for our function, we found m to be 2, now we need to find b

    • one year ago
  50. tjones89 Group Title
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    so we have y = 2x + b since we're given points we can substitute one in for the values of x and y, and then solve for b so if we use (0,1) as our point we get 1 = 2(0) + b so b = -1

    • one year ago
  51. tjones89 Group Title
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    and keep in mind that we could have used any of the points that were given for example if we used (2,5) we get 5 = 2(2) +b and again b = -1

    • one year ago
  52. tjones89 Group Title
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    so now that we know b, we can finally write the function as y = 2x -1

    • one year ago
  53. rebelchick777 Group Title
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    thank you.

    • one year ago
  54. tjones89 Group Title
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    np :)

    • one year ago
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