text: # Electrical Power - Cost of kW*hr
  
  ## Homework Statement
  
  An electric air conditioning unit draws 15 amps of direct current from a 134 V direct voltage source, and is used 24 hours a day during 21.1 days in July. How much will the electricity cost for the month if the local electrical rate is
  9.9 /kW· hr?
  
  (Note: sigfigs do not matter)
  
  ## Homework Equations
  
  P = I*$$\Delta$$V
  
  ## The Attempt at a Solution
  
  This seems like a straight forward question:
  
  P = 15*134 = 2010 W = 2.01 kW
  t = 21.1 days * 24 hours = 506.4 hours
  
  P*t = 1017.864 kW*hr
  
  Since units aren't given for 9.9, I tried for both dollars and cents:
  1017.864* 9.9 = $10076.85 1017.864*.099 =$100.785
  
  Both answers are wrong. I don't know where I'm making the mistake.
  
  Last edited:
  
  Related Introductory Physics Homework Help News on Phys.org
  mgb_phys
  Homework Helper
  The 9.9 is c/kwh, other than that you are correct, except for the slight typo on the last answer
  
  Looks like you might have made an arithmetic error when calculating in cents.
  
  1017.864*0.099 = 100.768
  
  berkeman
  Mentor
  Your last answer is correct. They want the answer of dolllars, with no cents. That's why they had such strange numbers (like 21.1 days).
  
  Your last answer is correct. They want the answer of dolllars, with no cents. That's why they had such strange numbers (like 21.1 days).
  Thank you so much. Removing cents gives the right answer.